diff --git a/lib/encryption/encryption.dart b/lib/encryption/encryption.dart
index ebcee139..78cee03b 100644
--- a/lib/encryption/encryption.dart
+++ b/lib/encryption/encryption.dart
@@ -62,7 +62,8 @@ class Encryption {
     crossSigning = CrossSigning(this);
   }
 
-  Future<void> init(String olmAccount) async {
+  // initial login passes null to init a new olm account
+  Future<void> init(String? olmAccount) async {
     await olmManager.init(olmAccount);
     _backgroundTasksRunning = true;
     _backgroundTasks(); // start the background tasks
@@ -86,7 +87,7 @@ class Encryption {
       );
 
   void handleDeviceOneTimeKeysCount(
-      Map<String, int> countJson, List<String> unusedFallbackKeyTypes) {
+      Map<String, int>? countJson, List<String>? unusedFallbackKeyTypes) {
     runInRoot(() => olmManager.handleDeviceOneTimeKeysCount(
         countJson, unusedFallbackKeyTypes));
   }
@@ -374,12 +375,13 @@ class Encryption {
 
   Future<void> autovalidateMasterOwnKey() async {
     // check if we can set our own master key as verified, if it isn't yet
-    final masterKey = client.userDeviceKeys[client.userID]?.masterKey;
+    final userId = client.userID;
+    final masterKey = client.userDeviceKeys[userId]?.masterKey;
     if (client.database != null &&
         masterKey != null &&
+        userId != null &&
         !masterKey.directVerified &&
-        masterKey
-            .hasValidSignatureChain(onlyValidateUserIds: {client.userID})) {
+        masterKey.hasValidSignatureChain(onlyValidateUserIds: {userId})) {
       await masterKey.setVerified(true);
     }
   }
diff --git a/lib/encryption/key_manager.dart b/lib/encryption/key_manager.dart
index ac56873a..45874747 100644
--- a/lib/encryption/key_manager.dart
+++ b/lib/encryption/key_manager.dart
@@ -95,6 +95,8 @@ class KeyManager {
   }) {
     final senderClaimedKeys_ = senderClaimedKeys ?? <String, String>{};
     final allowedAtIndex_ = allowedAtIndex ?? <String, Map<String, int>>{};
+    final userId = client.userID;
+    if (userId == null) return;
 
     if (!senderClaimedKeys_.containsKey('ed25519')) {
       final device = client.getUserDeviceKeysByCurve25519Key(senderKey);
@@ -126,7 +128,7 @@ class KeyManager {
       indexes: {},
       roomId: roomId,
       sessionId: sessionId,
-      key: client.userID,
+      key: userId,
       senderKey: senderKey,
       senderClaimedKeys: senderClaimedKeys_,
       allowedAtIndex: allowedAtIndex_,
@@ -157,7 +159,7 @@ class KeyManager {
         ?.storeInboundGroupSession(
       roomId,
       sessionId,
-      inboundGroupSession.pickle(client.userID),
+      inboundGroupSession.pickle(userId),
       json.encode(content),
       json.encode({}),
       json.encode(allowedAtIndex_),
@@ -169,7 +171,7 @@ class KeyManager {
         return;
       }
       if (uploaded) {
-        client.database.markInboundGroupSessionAsUploaded(roomId, sessionId);
+        client.database?.markInboundGroupSessionAsUploaded(roomId, sessionId);
       } else {
         _haveKeysToUpload = true;
       }
@@ -239,10 +241,10 @@ class KeyManager {
     }
     final session =
         await client.database?.getInboundGroupSession(roomId, sessionId);
-    if (session == null) {
-      return null;
-    }
-    final dbSess = SessionKey.fromDb(session, client.userID);
+    if (session == null) return null;
+    final userID = client.userID;
+    if (userID == null) return null;
+    final dbSess = SessionKey.fromDb(session, userID);
     final roomInboundGroupSessions =
         _inboundGroupSessions[roomId] ??= <String, SessionKey>{};
     if (!dbSess.isValid ||
@@ -394,12 +396,10 @@ class KeyManager {
                     sess.outboundGroupSession!.message_index();
               }
             }
-            if (client.database != null) {
-              await client.database.updateInboundGroupSessionAllowedAtIndex(
-                  json.encode(inboundSess!.allowedAtIndex),
-                  room.id,
-                  sess.outboundGroupSession!.session_id());
-            }
+            await client.database?.updateInboundGroupSessionAllowedAtIndex(
+                json.encode(inboundSess!.allowedAtIndex),
+                room.id,
+                sess.outboundGroupSession!.session_id());
             // send out the key
             await client.sendToDeviceEncryptedChunked(
                 devicesToReceive, EventTypes.RoomKey, rawSession);
@@ -422,9 +422,11 @@ class KeyManager {
   /// Store an outbound group session in the database
   Future<void> storeOutboundGroupSession(
       String roomId, OutboundGroupSession sess) async {
+    final userID = client.userID;
+    if (userID == null) return;
     await client.database?.storeOutboundGroupSession(
         roomId,
-        sess.outboundGroupSession!.pickle(client.userID),
+        sess.outboundGroupSession!.pickle(userID),
         json.encode(sess.devices),
         sess.creationTime.millisecondsSinceEpoch);
   }
@@ -464,6 +466,12 @@ class KeyManager {
       throw Exception(
           'Tried to create a megolm session in a non-existing room ($roomId)!');
     }
+    final userID = client.userID;
+    if (userID == null) {
+      throw Exception(
+          'Tried to create a megolm session without being logged in!');
+    }
+
     final deviceKeys = await room.getUserDeviceKeys();
     final deviceKeyIds = _getDeviceKeyIdMap(deviceKeys);
     deviceKeys.removeWhere((k) => !k.encryptToDevice);
@@ -498,7 +506,7 @@ class KeyManager {
       devices: deviceKeyIds,
       creationTime: DateTime.now(),
       outboundGroupSession: outboundGroupSession,
-      key: client.userID,
+      key: userID,
     );
     try {
       await client.sendToDeviceEncryptedChunked(
@@ -523,15 +531,18 @@ class KeyManager {
 
   /// Load an outbound group session from database
   Future<void> loadOutboundGroupSession(String roomId) async {
+    final database = client.database;
+    final userID = client.userID;
     if (_loadedOutboundGroupSessions.contains(roomId) ||
         _outboundGroupSessions.containsKey(roomId) ||
-        client.database == null) {
+        database == null ||
+        userID == null) {
       return; // nothing to do
     }
     _loadedOutboundGroupSessions.add(roomId);
-    final sess = await client.database.getOutboundGroupSession(
+    final sess = await database.getOutboundGroupSession(
       roomId,
-      client.userID,
+      userID,
     );
     if (sess == null || !sess.isValid) {
       return;
@@ -699,7 +710,9 @@ class KeyManager {
   bool _isUploadingKeys = false;
   bool _haveKeysToUpload = true;
   Future<void> backgroundTasks() async {
-    if (_isUploadingKeys || client.database == null) {
+    final database = client.database;
+    final userID = client.userID;
+    if (_isUploadingKeys || database == null || userID == null) {
       return;
     }
     _isUploadingKeys = true;
@@ -707,8 +720,7 @@ class KeyManager {
       if (!_haveKeysToUpload || !(await isCached())) {
         return; // we can't backup anyways
       }
-      final dbSessions =
-          await client.database.getInboundGroupSessionsToUpload();
+      final dbSessions = await database.getInboundGroupSessionsToUpload();
       if (dbSessions.isEmpty) {
         _haveKeysToUpload = false;
         return; // nothing to do
@@ -730,7 +742,7 @@ class KeyManager {
         final args = _GenerateUploadKeysArgs(
           pubkey: backupPubKey,
           dbSessions: <_DbInboundGroupSessionBundle>[],
-          userId: client.userID,
+          userId: userID,
         );
         // we need to calculate verified beforehand, as else we pass a closure to an isolate
         // with 500 keys they do, however, noticably block the UI, which is why we give brief async suspentions in here
@@ -741,7 +753,7 @@ class KeyManager {
               client.getUserDeviceKeysByCurve25519Key(dbSession.senderKey);
           args.dbSessions.add(_DbInboundGroupSessionBundle(
             dbSession: dbSession,
-            verified: device.verified,
+            verified: device?.verified ?? false,
           ));
           i++;
           if (i > 10) {
@@ -758,7 +770,7 @@ class KeyManager {
         // and now finally mark all the keys as uploaded
         // no need to optimze this, as we only run it so seldomly and almost never with many keys at once
         for (final dbSession in dbSessions) {
-          await client.database.markInboundGroupSessionAsUploaded(
+          await database.markInboundGroupSessionAsUploaded(
               dbSession.roomId, dbSession.sessionId);
         }
       } finally {
diff --git a/lib/encryption/key_verification_manager.dart b/lib/encryption/key_verification_manager.dart
index 2b1dbfb2..319f780e 100644
--- a/lib/encryption/key_verification_manager.dart
+++ b/lib/encryption/key_verification_manager.dart
@@ -56,7 +56,7 @@ class KeyVerificationManager {
 
   Future<void> handleToDeviceEvent(ToDeviceEvent event) async {
     if (!event.type.startsWith('m.key.verification.') ||
-        client.verificationMethods.isEmpty) {
+        client.verificationMethods.isEmpty != false) {
       return;
     }
     // we have key verification going on!
@@ -95,7 +95,7 @@ class KeyVerificationManager {
         : event['content']['msgtype'];
     if (type == null ||
         !type.startsWith('m.key.verification.') ||
-        client.verificationMethods.isEmpty) {
+        client.verificationMethods.isEmpty != false) {
       return;
     }
     if (type == EventTypes.KeyVerificationRequest) {
diff --git a/lib/encryption/olm_manager.dart b/lib/encryption/olm_manager.dart
index 6573be08..a99a1b6d 100644
--- a/lib/encryption/olm_manager.dart
+++ b/lib/encryption/olm_manager.dart
@@ -36,7 +36,7 @@ class OlmManager {
   /// Returns the base64 encoded keys to store them in a store.
   /// This String should **never** leave the device!
   String? get pickledOlmAccount =>
-      enabled ? _olmAccount!.pickle(client.userID) : null;
+      enabled ? _olmAccount!.pickle(client.userID!) : null;
   String? get fingerprintKey =>
       enabled ? json.decode(_olmAccount!.identity_keys())['ed25519'] : null;
   String? get identityKey =>
@@ -70,7 +70,7 @@ class OlmManager {
       try {
         await olm.init();
         _olmAccount = olm.Account();
-        _olmAccount!.unpickle(client.userID, olmAccount);
+        _olmAccount!.unpickle(client.userID!, olmAccount);
       } catch (_) {
         _olmAccount?.free();
         _olmAccount = null;
@@ -279,7 +279,7 @@ class OlmManager {
     // fixup accidental too many uploads. We delete only one of them so that the server has time to update the counts and because we will get rate limited anyway.
     if (keyCount > _olmAccount!.max_number_of_one_time_keys()) {
       final requestingKeysFrom = {
-        client.userID: {client.deviceID: 'signed_curve25519'}
+        client.userID!: {client.deviceID!: 'signed_curve25519'}
       };
       client.claimKeys(requestingKeysFrom, timeout: 10000);
     }
@@ -311,10 +311,7 @@ class OlmManager {
       // update an existing session
       _olmSessions[session.identityKey]![ix] = session;
     }
-    if (client.database == null) {
-      return;
-    }
-    await client.database.storeOlmSession(
+    await client.database?.storeOlmSession(
         session.identityKey,
         session.sessionId!,
         session.pickledSession!,
@@ -395,7 +392,7 @@ class OlmManager {
         client.database?.updateClientKeys(pickledOlmAccount!);
         plaintext = newSession.decrypt(type, body);
         runInRoot(() => storeOlmSession(OlmSession(
-              key: client.userID,
+              key: client.userID!,
               identityKey: senderKey,
               sessionId: newSession.session_id(),
               session: newSession,
@@ -428,25 +425,19 @@ class OlmManager {
   }
 
   Future<List<OlmSession>> getOlmSessionsFromDatabase(String senderKey) async {
-    if (client.database == null) {
-      return [];
-    }
     final olmSessions =
-        await client.database.getOlmSessions(senderKey, client.userID);
-    return olmSessions.where((sess) => sess.isValid).toList();
+        await client.database?.getOlmSessions(senderKey, client.userID!);
+    return olmSessions?.where((sess) => sess.isValid).toList() ?? [];
   }
 
   Future<void> getOlmSessionsForDevicesFromDatabase(
       List<String> senderKeys) async {
-    if (client.database == null) {
-      return;
-    }
-    final rows = await client.database.getOlmSessionsForDevices(
+    final rows = await client.database?.getOlmSessionsForDevices(
       senderKeys,
-      client.userID,
+      client.userID!,
     );
     final res = <String, List<OlmSession>>{};
-    for (final sess in rows) {
+    for (final sess in rows ?? []) {
       res[sess.identityKey] ??= <OlmSession>[];
       if (sess.isValid) {
         res[sess.identityKey]!.add(sess);
@@ -565,7 +556,7 @@ class OlmManager {
             session.create_outbound(
                 _olmAccount!, identityKey, deviceKey['key']);
             await storeOlmSession(OlmSession(
-              key: client.userID,
+              key: client.userID!,
               identityKey: identityKey,
               sessionId: session.session_id(),
               session: session,
@@ -602,7 +593,7 @@ class OlmManager {
     await storeOlmSession(sess.first);
     if (client.database != null) {
       // ignore: unawaited_futures
-      runInRoot(() => client.database.setLastSentMessageUserDeviceKey(
+      runInRoot(() => client.database?.setLastSentMessageUserDeviceKey(
           json.encode({
             'type': type,
             'content': payload,
@@ -668,8 +659,10 @@ class OlmManager {
       Logs().v(
           '[OlmManager] Device ${device.userId}:${device.deviceId} generated a new olm session, replaying last sent message...');
       final lastSentMessageRes = await client.database
-          .getLastSentMessageUserDeviceKey(device.userId, device.deviceId!);
-      if (lastSentMessageRes.isEmpty || (lastSentMessageRes.first.isEmpty)) {
+          ?.getLastSentMessageUserDeviceKey(device.userId, device.deviceId!);
+      if (lastSentMessageRes == null ||
+          lastSentMessageRes.isEmpty ||
+          lastSentMessageRes.first.isEmpty) {
         return;
       }
       final lastSentMessage = json.decode(lastSentMessageRes.first);
diff --git a/lib/encryption/ssss.dart b/lib/encryption/ssss.dart
index e741dbb2..3a8a380f 100644
--- a/lib/encryption/ssss.dart
+++ b/lib/encryption/ssss.dart
@@ -187,7 +187,7 @@ class SSSS {
 
   Future<void> setDefaultKeyId(String keyId) async {
     await client.setAccountData(
-      client.userID,
+      client.userID!,
       EventTypes.SecretStorageDefaultKey,
       SecretStorageDefaultKeyContent(key: keyId).toJson(),
     );
@@ -250,7 +250,7 @@ class SSSS {
         syncUpdate.accountData!
             .any((accountData) => accountData.type == accountDataType));
     await client.setAccountData(
-        client.userID, accountDataType, content.toJson());
+        client.userID!, accountDataType, content.toJson());
     await waitForAccountData;
 
     final key = open(keyId);
@@ -295,7 +295,7 @@ class SSSS {
     if (_cache.containsKey(type) && isValid(_cache[type])) {
       return _cache[type]?.content;
     }
-    final ret = await client.database.getSSSSCache(type);
+    final ret = await client.database?.getSSSSCache(type);
     if (ret == null) {
       return null;
     }
@@ -321,10 +321,10 @@ class SSSS {
     final encryptInfo = _Encrypted(
         iv: enc['iv'], ciphertext: enc['ciphertext'], mac: enc['mac']);
     final decrypted = await decryptAes(encryptInfo, key, type);
-    if (cacheTypes.contains(type) && client.database != null) {
+    final db = client.database;
+    if (cacheTypes.contains(type) && db != null) {
       // cache the thing
-      await client.database
-          .storeSSSSCache(type, keyId, enc['ciphertext'], decrypted);
+      await db.storeSSSSCache(type, keyId, enc['ciphertext'], decrypted);
       if (_cacheCallbacks.containsKey(type) && await getCached(type) == null) {
         _cacheCallbacks[type]!(decrypted);
       }
@@ -351,11 +351,11 @@ class SSSS {
       'mac': encrypted.mac,
     };
     // store the thing in your account data
-    await client.setAccountData(client.userID, type, content);
-    if (cacheTypes.contains(type) && client.database != null) {
+    await client.setAccountData(client.userID!, type, content);
+    final db = client.database;
+    if (cacheTypes.contains(type) && db != null) {
       // cache the thing
-      await client.database
-          .storeSSSSCache(type, keyId, encrypted.ciphertext, secret);
+      await db.storeSSSSCache(type, keyId, encrypted.ciphertext, secret);
       if (_cacheCallbacks.containsKey(type) && await getCached(type) == null) {
         _cacheCallbacks[type]!(secret);
       }
@@ -381,10 +381,10 @@ class SSSS {
       throw Exception('Secrets do not match up!');
     }
     // store the thing in your account data
-    await client.setAccountData(client.userID, type, content);
-    if (cacheTypes.contains(type) && client.database != null) {
+    await client.setAccountData(client.userID!, type, content);
+    if (cacheTypes.contains(type)) {
       // cache the thing
-      await client.database.storeSSSSCache(
+      await client.database?.storeSSSSCache(
           type, keyId, content['encrypted'][keyId]['ciphertext'], secret);
     }
   }
@@ -542,13 +542,13 @@ class SSSS {
         return; // our request is more than 15min in the past...better not trust it anymore
       }
       Logs().i('[SSSS] Secret for type ${request.type} is ok, storing it');
-      if (client.database != null) {
+      final db = client.database;
+      if (db != null) {
         final keyId = keyIdFromType(request.type);
         if (keyId != null) {
           final ciphertext = client.accountData[request.type]!
               .content['encrypted'][keyId]['ciphertext'];
-          await client.database
-              .storeSSSSCache(request.type, keyId, ciphertext, secret);
+          await db.storeSSSSCache(request.type, keyId, ciphertext, secret);
           if (_cacheCallbacks.containsKey(request.type)) {
             _cacheCallbacks[request.type]!(secret);
           }
diff --git a/lib/encryption/utils/bootstrap.dart b/lib/encryption/utils/bootstrap.dart
index e784d900..aef6518c 100644
--- a/lib/encryption/utils/bootstrap.dart
+++ b/lib/encryption/utils/bootstrap.dart
@@ -357,6 +357,7 @@ class Bootstrap {
       checkOnlineKeyBackup();
       return;
     }
+    final userID = client.userID!;
     try {
       Uint8List masterSigningKey;
       final secretsToStore = <String, String>{};
@@ -370,7 +371,7 @@ class Bootstrap {
           masterSigningKey = master.generate_seed();
           masterPub = master.init_with_seed(masterSigningKey);
           final json = <String, dynamic>{
-            'user_id': client.userID,
+            'user_id': userID,
             'usage': ['master'],
             'keys': <String, dynamic>{
               'ed25519:$masterPub': masterPub,
@@ -414,7 +415,7 @@ class Bootstrap {
           final selfSigningPriv = selfSigning.generate_seed();
           final selfSigningPub = selfSigning.init_with_seed(selfSigningPriv);
           final json = <String, dynamic>{
-            'user_id': client.userID,
+            'user_id': userID,
             'usage': ['self_signing'],
             'keys': <String, dynamic>{
               'ed25519:$selfSigningPub': selfSigningPub,
@@ -422,7 +423,7 @@ class Bootstrap {
           };
           final signature = _sign(json);
           json['signatures'] = <String, dynamic>{
-            client.userID: <String, dynamic>{
+            userID: <String, dynamic>{
               'ed25519:$masterPub': signature,
             },
           };
@@ -439,7 +440,7 @@ class Bootstrap {
           final userSigningPriv = userSigning.generate_seed();
           final userSigningPub = userSigning.init_with_seed(userSigningPriv);
           final json = <String, dynamic>{
-            'user_id': client.userID,
+            'user_id': userID,
             'usage': ['user_signing'],
             'keys': <String, dynamic>{
               'ed25519:$userSigningPub': userSigningPub,
@@ -447,7 +448,7 @@ class Bootstrap {
           };
           final signature = _sign(json);
           json['signatures'] = <String, dynamic>{
-            client.userID: <String, dynamic>{
+            userID: <String, dynamic>{
               'ed25519:$masterPub': signature,
             },
           };
@@ -462,7 +463,7 @@ class Bootstrap {
       state = BootstrapState.loading;
       Logs().v('Upload device signing keys.');
       await client.uiaRequestBackground(
-          (AuthenticationData auth) => client.uploadCrossSigningKeys(
+          (AuthenticationData? auth) => client.uploadCrossSigningKeys(
                 masterKey: masterKey,
                 selfSigningKey: selfSigningKey,
                 userSigningKey: userSigningKey,
diff --git a/lib/encryption/utils/key_verification.dart b/lib/encryption/utils/key_verification.dart
index 449568ac..10fe9946 100644
--- a/lib/encryption/utils/key_verification.dart
+++ b/lib/encryption/utils/key_verification.dart
@@ -152,8 +152,10 @@ class KeyVerification {
 
   List<String> get knownVerificationMethods {
     final methods = <String>[];
-    if (client.verificationMethods.contains(KeyVerificationMethod.numbers) ||
-        client.verificationMethods.contains(KeyVerificationMethod.emoji)) {
+    if (client.verificationMethods?.contains(KeyVerificationMethod.numbers) ==
+            true ||
+        client.verificationMethods?.contains(KeyVerificationMethod.emoji) ==
+            true) {
       methods.add('m.sas.v1');
     }
     return methods;
@@ -673,11 +675,13 @@ class _KeyVerificationMethodSas extends _KeyVerificationMethod {
   List<String> get knownAuthentificationTypes {
     final types = <String>[];
     if (request.client.verificationMethods
-        .contains(KeyVerificationMethod.emoji)) {
+            ?.contains(KeyVerificationMethod.emoji) ==
+        true) {
       types.add('emoji');
     }
     if (request.client.verificationMethods
-        .contains(KeyVerificationMethod.numbers)) {
+            ?.contains(KeyVerificationMethod.numbers) ==
+        true) {
       types.add('decimal');
     }
     return types;
@@ -876,7 +880,7 @@ class _KeyVerificationMethodSas extends _KeyVerificationMethod {
               : theirInfo + ourInfo) +
           request.transactionId!;
     } else if (keyAgreementProtocol == 'curve25519') {
-      final ourInfo = client.userID + client.deviceID;
+      final ourInfo = client.userID! + client.deviceID!;
       final theirInfo = request.userId + request.deviceId!;
       sasInfo = 'MATRIX_KEY_VERIFICATION_SAS' +
           (request.startedVerification
@@ -891,8 +895,8 @@ class _KeyVerificationMethodSas extends _KeyVerificationMethod {
 
   Future<void> _sendMac() async {
     final baseInfo = 'MATRIX_KEY_VERIFICATION_MAC' +
-        client.userID +
-        client.deviceID +
+        client.userID! +
+        client.deviceID! +
         request.userId +
         request.deviceId! +
         request.transactionId!;
@@ -929,8 +933,8 @@ class _KeyVerificationMethodSas extends _KeyVerificationMethod {
     final baseInfo = 'MATRIX_KEY_VERIFICATION_MAC' +
         request.userId +
         request.deviceId! +
-        client.userID +
-        client.deviceID +
+        client.userID! +
+        client.deviceID! +
         request.transactionId!;
 
     final keyList = payload['mac'].keys.toList();
diff --git a/lib/src/client.dart b/lib/src/client.dart
index 4dbbb3dd..75ff1d87 100644
--- a/lib/src/client.dart
+++ b/lib/src/client.dart
@@ -1,4 +1,3 @@
-// @dart=2.9
 /*
  *   Famedly Matrix SDK
  *   Copyright (C) 2019, 2020, 2021 Famedly GmbH
@@ -26,6 +25,7 @@ import 'package:http/http.dart' as http;
 import 'package:matrix/src/utils/run_in_root.dart';
 import 'package:mime/mime.dart';
 import 'package:olm/olm.dart' as olm;
+import 'package:collection/collection.dart' show IterableExtension;
 
 import '../encryption.dart';
 import '../matrix.dart';
@@ -56,28 +56,28 @@ extension TrailingSlash on Uri {
 /// [Matrix](https://matrix.org) homeserver and is the entry point for this
 /// SDK.
 class Client extends MatrixApi {
-  int _id;
+  int? _id;
 
   // Keeps track of the currently ongoing syncRequest
   // in case we want to cancel it.
-  int _currentSyncId;
+  int _currentSyncId = -1;
 
-  int get id => _id;
+  int? get id => _id;
 
-  final FutureOr<DatabaseApi> Function(Client) databaseBuilder;
-  final FutureOr<DatabaseApi> Function(Client) legacyDatabaseBuilder;
-  final FutureOr<void> Function(Client) databaseDestroyer;
-  final FutureOr<void> Function(Client) legacyDatabaseDestroyer;
-  DatabaseApi _database;
+  final FutureOr<DatabaseApi> Function(Client)? databaseBuilder;
+  final FutureOr<DatabaseApi> Function(Client)? legacyDatabaseBuilder;
+  final FutureOr<void> Function(Client)? databaseDestroyer;
+  final FutureOr<void> Function(Client)? legacyDatabaseDestroyer;
+  DatabaseApi? _database;
 
-  DatabaseApi get database => _database;
+  DatabaseApi? get database => _database;
 
   bool enableE2eeRecovery;
 
   @deprecated
   MatrixApi get api => this;
 
-  Encryption encryption;
+  Encryption? encryption;
 
   Set<KeyVerificationMethod> verificationMethods;
 
@@ -96,16 +96,17 @@ class Client extends MatrixApi {
   bool mxidLocalPartFallback = true;
 
   // For CommandsClientExtension
-  final Map<String, FutureOr<String> Function(CommandArgs)> commands = {};
+  final Map<String, FutureOr<String?> Function(CommandArgs)> commands = {};
   final Filter syncFilter;
 
-  String syncFilterId;
+  String? syncFilterId;
 
   final Future<R> Function<Q, R>(FutureOr<R> Function(Q), Q,
-      {String debugLabel}) compute;
+      {String debugLabel})? compute;
 
   Future<T> runInBackground<T, U>(
       FutureOr<T> Function(U arg) function, U arg) async {
+    final compute = this.compute;
     if (compute != null) {
       return await compute(function, arg);
     }
@@ -155,30 +156,33 @@ class Client extends MatrixApi {
     this.legacyDatabaseBuilder,
     this.legacyDatabaseDestroyer,
     this.enableE2eeRecovery = false,
-    this.verificationMethods,
-    http.Client httpClient,
-    this.importantStateEvents,
-    this.roomPreviewLastEvents,
+    Set<KeyVerificationMethod>? verificationMethods,
+    http.Client? httpClient,
+    Set<String>? importantStateEvents,
+    Set<String>? roomPreviewLastEvents,
     this.pinUnreadRooms = false,
     this.pinInvitedRooms = true,
     this.sendMessageTimeoutSeconds = 60,
     this.requestHistoryOnLimitedTimeline = false,
-    this.supportedLoginTypes,
+    Set<String>? supportedLoginTypes,
     this.compute,
-    Filter syncFilter,
-    @deprecated bool debug,
+    Filter? syncFilter,
+    @deprecated bool? debug,
   })  : syncFilter = syncFilter ??
             Filter(
               room: RoomFilter(
                 state: StateFilter(lazyLoadMembers: true),
               ),
             ),
+        importantStateEvents = importantStateEvents ??= {},
+        roomPreviewLastEvents = roomPreviewLastEvents ??= {},
+        supportedLoginTypes =
+            supportedLoginTypes ?? {AuthenticationTypes.password},
+        __loginState = LoginState.loggedOut,
+        verificationMethods = verificationMethods ?? <KeyVerificationMethod>{},
         super(
             httpClient:
                 VariableTimeoutHttpClient(httpClient ?? http.Client())) {
-    supportedLoginTypes ??= {AuthenticationTypes.password};
-    verificationMethods ??= <KeyVerificationMethod>{};
-    importantStateEvents ??= {};
     importantStateEvents.addAll([
       EventTypes.RoomName,
       EventTypes.RoomAvatar,
@@ -191,7 +195,6 @@ class Client extends MatrixApi {
       EventTypes.spaceParent,
       EventTypes.RoomCreate,
     ]);
-    roomPreviewLastEvents ??= {};
     roomPreviewLastEvents.addAll([
       EventTypes.Message,
       EventTypes.Encrypted,
@@ -206,19 +209,19 @@ class Client extends MatrixApi {
   final String clientName;
 
   /// The Matrix ID of the current logged user.
-  String get userID => _userID;
-  String _userID;
+  String? get userID => _userID;
+  String? _userID;
 
   /// This points to the position in the synchronization history.
-  String prevBatch;
+  String? prevBatch;
 
   /// The device ID is an unique identifier for this device.
-  String get deviceID => _deviceID;
-  String _deviceID;
+  String? get deviceID => _deviceID;
+  String? _deviceID;
 
   /// The device name is a human readable identifier for this device.
-  String get deviceName => _deviceName;
-  String _deviceName;
+  String? get deviceName => _deviceName;
+  String? _deviceName;
 
   /// Returns the current login state.
   LoginState get loginState => __loginState;
@@ -235,7 +238,7 @@ class Client extends MatrixApi {
   List<Room> _rooms = [];
 
   /// Whether this client supports end-to-end encryption using olm.
-  bool get encryptionEnabled => encryption != null && encryption.enabled;
+  bool get encryptionEnabled => encryption?.enabled == true;
 
   /// Whether this client is able to encrypt and decrypt files.
   bool get fileEncryptionEnabled => encryptionEnabled && true;
@@ -246,9 +249,7 @@ class Client extends MatrixApi {
 
   /// Wheather this session is unknown to others
   bool get isUnknownSession =>
-      !userDeviceKeys.containsKey(userID) ||
-      !userDeviceKeys[userID].deviceKeys.containsKey(deviceID) ||
-      !userDeviceKeys[userID].deviceKeys[deviceID].signed;
+      userDeviceKeys[userID]?.deviceKeys[deviceID]?.signed != true;
 
   /// Warning! This endpoint is for testing only!
   set rooms(List<Room> newList) {
@@ -269,7 +270,7 @@ class Client extends MatrixApi {
     return '$clientName-$_transactionCounter-${DateTime.now().millisecondsSinceEpoch}';
   }
 
-  Room getRoomByAlias(String alias) {
+  Room? getRoomByAlias(String alias) {
     for (final room in rooms) {
       if (room.canonicalAlias == alias) return room;
     }
@@ -279,7 +280,7 @@ class Client extends MatrixApi {
   /// Searches in the local cache for the given room and returns null if not
   /// found. If you have loaded the [loadArchive()] before, it can also return
   /// archived rooms.
-  Room getRoomById(String id) {
+  Room? getRoomById(String id) {
     for (final room in <Room>[...rooms, ..._archivedRooms]) {
       if (room.id == id) return room;
     }
@@ -288,30 +289,29 @@ class Client extends MatrixApi {
   }
 
   Map<String, dynamic> get directChats =>
-      accountData['m.direct'] != null ? accountData['m.direct'].content : {};
+      accountData['m.direct']?.content ?? {};
 
   /// Returns the (first) room ID from the store which is a private chat with the user [userId].
   /// Returns null if there is none.
-  String getDirectChatFromUserId(String userId) {
-    if (accountData['m.direct'] != null &&
-        accountData['m.direct'].content[userId] is List<dynamic> &&
-        accountData['m.direct'].content[userId].length > 0) {
-      final potentialRooms = accountData['m.direct']
-          .content[userId]
+  String? getDirectChatFromUserId(String userId) {
+    final directChats = accountData['m.direct']?.content[userId];
+    if (directChats is List<dynamic> && directChats.isNotEmpty) {
+      final potentialRooms = directChats
           .cast<String>()
           .map(getRoomById)
           .where((room) => room != null && room.membership == Membership.join);
       if (potentialRooms.isNotEmpty) {
-        return potentialRooms
-            .fold(
-                null,
-                (prev, r) => prev == null
-                    ? r
-                    : (prev.lastEvent.originServerTs.millisecondsSinceEpoch <
-                            r.lastEvent.originServerTs.millisecondsSinceEpoch
-                        ? r
-                        : prev))
-            .id;
+        return potentialRooms.fold<Room>(potentialRooms.first!,
+            (Room prev, Room? r) {
+          if (r == null) {
+            return prev;
+          }
+          final prevLast =
+              prev.lastEvent?.originServerTs.millisecondsSinceEpoch ?? 0;
+          final rLast = r.lastEvent?.originServerTs.millisecondsSinceEpoch ?? 0;
+
+          return rLast > prevLast ? r : prev;
+        }).id;
       }
     }
     for (final room in rooms) {
@@ -330,8 +330,8 @@ class Client extends MatrixApi {
     String MatrixIdOrDomain,
   ) async {
     try {
-      final response = await http.get(
-          Uri.https(MatrixIdOrDomain.domain, '/.well-known/matrix/client'));
+      final response = await http.get(Uri.https(
+          MatrixIdOrDomain.domain ?? '', '/.well-known/matrix/client'));
       var respBody = response.body;
       try {
         respBody = utf8.decode(response.bodyBytes);
@@ -345,7 +345,7 @@ class Client extends MatrixApi {
       // provide a reasonable fallback.
       return DiscoveryInformation(
         mHomeserver: HomeserverInformation(
-            baseUrl: Uri.https(MatrixIdOrDomain.domain, '')),
+            baseUrl: Uri.https(MatrixIdOrDomain.domain ?? '', '')),
       );
     }
   }
@@ -364,19 +364,20 @@ class Client extends MatrixApi {
   /// login types. Throws an exception if the server is not compatible with the
   /// client and sets [homeserver] to [homeserverUrl] if it is. Supports the
   /// types `Uri` and `String`.
-  Future<DiscoveryInformation> checkHomeserver(dynamic homeserverUrl,
+  Future<DiscoveryInformation?> checkHomeserver(dynamic homeserverUrl,
       {bool checkWellKnown = true}) async {
     try {
-      homeserver =
+      var homeserver = this.homeserver =
           (homeserverUrl is Uri) ? homeserverUrl : Uri.parse(homeserverUrl);
-      homeserver = homeserver.stripTrailingSlash();
+      homeserver = this.homeserver = homeserver.stripTrailingSlash();
 
       // Look up well known
-      DiscoveryInformation wellKnown;
+      DiscoveryInformation? wellKnown;
       if (checkWellKnown) {
         try {
           wellKnown = await getWellknown();
-          homeserver = wellKnown.mHomeserver.baseUrl.stripTrailingSlash();
+          homeserver = this.homeserver =
+              wellKnown.mHomeserver.baseUrl.stripTrailingSlash();
         } catch (e) {
           Logs().v('Found no well known information', e);
         }
@@ -390,10 +391,10 @@ class Client extends MatrixApi {
             versions.versions.toSet(), supportedVersions);
       }
 
-      final loginTypes = await getLoginFlows();
+      final loginTypes = await getLoginFlows() ?? [];
       if (!loginTypes.any((f) => supportedLoginTypes.contains(f.type))) {
         throw BadServerLoginTypesException(
-            loginTypes.map((f) => f.type).toSet(), supportedLoginTypes);
+            loginTypes.map((f) => f.type ?? '').toSet(), supportedLoginTypes);
       }
 
       return wellKnown;
@@ -408,13 +409,13 @@ class Client extends MatrixApi {
   /// You have to call [checkHomeserver] first to set a homeserver.
   @override
   Future<RegisterResponse> register({
-    String username,
-    String password,
-    String deviceId,
-    String initialDeviceDisplayName,
-    bool inhibitLogin,
-    AuthenticationData auth,
-    AccountKind kind,
+    String? username,
+    String? password,
+    String? deviceId,
+    String? initialDeviceDisplayName,
+    bool? inhibitLogin,
+    AuthenticationData? auth,
+    AccountKind? kind,
   }) async {
     final response = await super.register(
       username: username,
@@ -426,17 +427,23 @@ class Client extends MatrixApi {
     );
 
     // Connect if there is an access token in the response.
-    if (response.accessToken == null ||
-        response.deviceId == null ||
-        response.userId == null) {
-      throw Exception('Registered but token, device ID or user ID is null.');
+    final accessToken = response.accessToken;
+    final deviceId_ = response.deviceId;
+    final userId = response.userId;
+    final homeserver = this.homeserver;
+    if (accessToken == null ||
+        deviceId_ == null ||
+        userId == null ||
+        homeserver == null) {
+      throw Exception(
+          'Registered but token, device ID, user ID or homeserver is null.');
     }
     await init(
-        newToken: response.accessToken,
-        newUserID: response.userId,
+        newToken: accessToken,
+        newUserID: userId,
         newHomeserver: homeserver,
         newDeviceName: initialDeviceDisplayName ?? '',
-        newDeviceID: response.deviceId);
+        newDeviceID: deviceId_);
     return response;
   }
 
@@ -450,20 +457,20 @@ class Client extends MatrixApi {
   @override
   Future<LoginResponse> login(
     LoginType type, {
-    AuthenticationIdentifier identifier,
-    String password,
-    String token,
-    String deviceId,
-    String initialDeviceDisplayName,
-    AuthenticationData auth,
-    @Deprecated('Deprecated in favour of identifier.') String user,
-    @Deprecated('Deprecated in favour of identifier.') String medium,
-    @Deprecated('Deprecated in favour of identifier.') String address,
+    AuthenticationIdentifier? identifier,
+    String? password,
+    String? token,
+    String? deviceId,
+    String? initialDeviceDisplayName,
+    AuthenticationData? auth,
+    @Deprecated('Deprecated in favour of identifier.') String? user,
+    @Deprecated('Deprecated in favour of identifier.') String? medium,
+    @Deprecated('Deprecated in favour of identifier.') String? address,
   }) async {
-    if (homeserver == null && user.isValidMatrixId) {
+    if (homeserver == null && user != null && user.isValidMatrixId == true) {
       await checkHomeserver(user.domain);
     }
-    final loginResp = await super.login(
+    final response = await super.login(
       type,
       identifier: identifier,
       password: password,
@@ -479,19 +486,24 @@ class Client extends MatrixApi {
     );
 
     // Connect if there is an access token in the response.
-    if (loginResp.accessToken == null ||
-        loginResp.deviceId == null ||
-        loginResp.userId == null) {
+    final accessToken = response.accessToken;
+    final deviceId_ = response.deviceId;
+    final userId = response.userId;
+    final homeserver_ = homeserver;
+    if (accessToken == null ||
+        deviceId_ == null ||
+        userId == null ||
+        homeserver_ == null) {
       throw Exception('Registered but token, device ID or user ID is null.');
     }
     await init(
-      newToken: loginResp.accessToken,
-      newUserID: loginResp.userId,
-      newHomeserver: homeserver,
+      newToken: accessToken,
+      newUserID: userId,
+      newHomeserver: homeserver_,
       newDeviceName: initialDeviceDisplayName ?? '',
-      newDeviceID: loginResp.deviceId,
+      newDeviceID: deviceId_,
     );
-    return loginResp;
+    return response;
   }
 
   /// Sends a logout command to the homeserver and clears all local data,
@@ -524,18 +536,20 @@ class Client extends MatrixApi {
 
   /// Run any request and react on user interactive authentication flows here.
   Future<T> uiaRequestBackground<T>(
-      Future<T> Function(AuthenticationData auth) request) {
+      Future<T> Function(AuthenticationData? auth) request) {
     final completer = Completer<T>();
-    UiaRequest uia;
+    UiaRequest? uia;
     uia = UiaRequest(
       request: request,
       onUpdate: (state) {
-        if (state == UiaRequestState.done) {
-          completer.complete(uia.result);
-        } else if (state == UiaRequestState.fail) {
-          completer.completeError(uia.error);
-        } else {
-          onUiaRequest.add(uia);
+        if (uia != null) {
+          if (state == UiaRequestState.done) {
+            completer.complete(uia.result);
+          } else if (state == UiaRequestState.fail) {
+            completer.completeError(uia.error!);
+          } else {
+            onUiaRequest.add(uia);
+          }
         }
       },
     );
@@ -571,13 +585,13 @@ class Client extends MatrixApi {
   ///
   /// https://github.com/matrix-org/matrix-doc/blob/matthew/msc1772/proposals/1772-groups-as-rooms.md
   Future<String> createSpace({
-    String name,
-    String topic,
+    String? name,
+    String? topic,
     Visibility visibility = Visibility.public,
-    String spaceAliasName,
-    List<String> invite,
-    List<Invite3pid> invite3pid,
-    String roomVersion,
+    String? spaceAliasName,
+    List<String>? invite,
+    List<Invite3pid>? invite3pid,
+    String? roomVersion,
   }) =>
       createRoom(
         name: name,
@@ -604,7 +618,7 @@ class Client extends MatrixApi {
       }
       if (profileSet.length == 1) return profileSet.first;
     }
-    return getProfileFromUserId(userID);
+    return getProfileFromUserId(userID!);
   }
 
   final Map<String, ProfileInformation> _profileCache = {};
@@ -619,13 +633,9 @@ class Client extends MatrixApi {
   Future<Profile> getProfileFromUserId(String userId,
       {bool cache = true, bool getFromRooms = true}) async {
     if (getFromRooms) {
-      final room = rooms.firstWhere(
-          (Room room) =>
-              room
-                  .getParticipants()
-                  .indexWhere((User user) => user.id == userId) !=
-              -1,
-          orElse: () => null);
+      final room = rooms.firstWhereOrNull((Room room) =>
+          room.getParticipants().indexWhere((User user) => user.id == userId) !=
+          -1);
       if (room != null) {
         final user =
             room.getParticipants().firstWhere((User user) => user.id == userId);
@@ -635,14 +645,15 @@ class Client extends MatrixApi {
             avatarUrl: user.avatarUrl);
       }
     }
-    if (cache && _profileCache.containsKey(userId)) {
-      final profile = _profileCache[userId];
+
+    var profile = _profileCache[userId];
+    if (cache && profile != null) {
       return Profile(
           userId: userId,
           displayName: profile.displayname,
           avatarUrl: profile.avatarUrl);
     }
-    final profile = await getUserProfile(userId);
+    profile = await getUserProfile(userId);
     _profileCache[userId] = profile;
     return Profile(
         userId: userId,
@@ -661,8 +672,10 @@ class Client extends MatrixApi {
       filter: '{"room":{"include_leave":true,"timeline":{"limit":10}}}',
       timeout: 0,
     );
-    if (syncResp.rooms?.leave != null) {
-      for (final entry in syncResp.rooms.leave.entries) {
+
+    final leave = syncResp.rooms?.leave;
+    if (leave != null) {
+      for (final entry in leave.entries) {
         final id = entry.key;
         final room = entry.value;
         final leftRoom = Room(
@@ -670,25 +683,22 @@ class Client extends MatrixApi {
           membership: Membership.leave,
           client: this,
           roomAccountData:
-              room.accountData?.asMap()?.map((k, v) => MapEntry(v.type, v)) ??
+              room.accountData?.asMap().map((k, v) => MapEntry(v.type, v)) ??
                   <String, BasicRoomEvent>{},
         );
-        if (room.timeline?.events != null) {
-          for (final event in room.timeline.events) {
-            leftRoom.setState(Event.fromMatrixEvent(
-              event,
-              leftRoom,
-            ));
-          }
-        }
-        if (room.state != null) {
-          for (final event in room.state) {
-            leftRoom.setState(Event.fromMatrixEvent(
-              event,
-              leftRoom,
-            ));
-          }
-        }
+
+        room.timeline?.events?.forEach((event) {
+          leftRoom.setState(Event.fromMatrixEvent(
+            event,
+            leftRoom,
+          ));
+        });
+        room.state?.forEach((event) {
+          leftRoom.setState(Event.fromMatrixEvent(
+            event,
+            leftRoom,
+          ));
+        });
         _archivedRooms.add(leftRoom);
       }
     }
@@ -699,12 +709,13 @@ class Client extends MatrixApi {
   /// and returns the mxc url.
   @override
   Future<Uri> uploadContent(Uint8List file,
-      {String filename, String contentType}) async {
+      {String? filename, String? contentType}) async {
     contentType ??= lookupMimeType(filename ?? '', headerBytes: file);
     final mxc = await super
         .uploadContent(file, filename: filename, contentType: contentType);
-    final storeable = database != null && file.length <= database.maxFileSize;
-    if (storeable) {
+
+    final database = this.database;
+    if (database != null && file.length <= database.maxFileSize) {
       await database.storeFile(
           mxc, file, DateTime.now().millisecondsSinceEpoch);
     }
@@ -717,13 +728,13 @@ class Client extends MatrixApi {
     String userId,
     String roomId,
     bool typing, {
-    int timeout,
+    int? timeout,
   }) async {
     await super.setTyping(userId, roomId, typing, timeout: timeout);
     final room = getRoomById(roomId);
     if (typing && room != null && encryptionEnabled && room.encrypted) {
       // ignore: unawaited_futures
-      encryption.keyManager.prepareOutboundGroupSession(roomId);
+      encryption?.keyManager.prepareOutboundGroupSession(roomId);
     }
   }
 
@@ -734,19 +745,21 @@ class Client extends MatrixApi {
       filename: file.name,
       contentType: file.mimeType,
     );
-    await setAvatarUrl(userID, uploadResp);
+    await setAvatarUrl(userID!, uploadResp);
     return;
   }
 
   /// Returns the global push rules for the logged in user.
-  PushRuleSet get globalPushRules => accountData.containsKey('m.push_rules')
-      ? PushRuleSet.fromJson(accountData['m.push_rules'].content['global'])
-      : null;
+  PushRuleSet? get globalPushRules {
+    final pushrules = accountData['m.push_rules']?.content['global'];
+    return pushrules != null ? PushRuleSet.fromJson(pushrules) : null;
+  }
 
   /// Returns the device push rules for the logged in user.
-  PushRuleSet get devicePushRules => accountData.containsKey('m.push_rules')
-      ? PushRuleSet.fromJson(accountData['m.push_rules'].content['device'])
-      : null;
+  PushRuleSet? get devicePushRules {
+    final pushrules = accountData['m.push_rules']?.content['device'];
+    return pushrules != null ? PushRuleSet.fromJson(pushrules) : null;
+  }
 
   static const Set<String> supportedVersions = {'r0.5.0', 'r0.6.0'};
   static const List<String> supportedDirectEncryptionAlgorithms = [
@@ -848,12 +861,12 @@ class Client extends MatrixApi {
 
   @Deprecated('Use init() instead')
   void connect({
-    String newToken,
-    Uri newHomeserver,
-    String newUserID,
-    String newDeviceName,
-    String newDeviceID,
-    String newOlmAccount,
+    String? newToken,
+    Uri? newHomeserver,
+    String? newUserID,
+    String? newDeviceName,
+    String? newDeviceID,
+    String? newOlmAccount,
   }) =>
       init(
         newToken: newToken,
@@ -880,12 +893,12 @@ class Client extends MatrixApi {
   /// all of them must be set! If you don't set them, this method will try to
   /// get them from the database.
   Future<void> init({
-    String newToken,
-    Uri newHomeserver,
-    String newUserID,
-    String newDeviceName,
-    String newDeviceID,
-    String newOlmAccount,
+    String? newToken,
+    Uri? newHomeserver,
+    String? newUserID,
+    String? newDeviceName,
+    String? newDeviceID,
+    String? newOlmAccount,
     bool waitForFirstSync = true,
   }) async {
     if ((newToken != null ||
@@ -909,35 +922,35 @@ class Client extends MatrixApi {
       }
 
       if (databaseBuilder != null) {
-        _database ??= await databaseBuilder(this);
+        _database ??= await databaseBuilder?.call(this);
       }
 
-      String olmAccount;
-      if (database != null) {
-        final account = await database.getClient(clientName);
-        if (account != null) {
-          _id = account['client_id'];
-          homeserver = Uri.parse(account['homeserver_url']);
-          accessToken = account['token'];
-          _userID = account['user_id'];
-          _deviceID = account['device_id'];
-          _deviceName = account['device_name'];
-          syncFilterId = account['sync_filter_id'];
-          prevBatch = account['prev_batch'];
-          olmAccount = account['olm_account'];
-        }
+      String? olmAccount;
+      String? accessToken;
+      String? _userID;
+      final account = await this.database?.getClient(clientName);
+      if (account != null) {
+        _id = account['client_id'];
+        homeserver = Uri.parse(account['homeserver_url']);
+        accessToken = this.accessToken = account['token'];
+        _userID = this._userID = account['user_id'];
+        _deviceID = account['device_id'];
+        _deviceName = account['device_name'];
+        syncFilterId = account['sync_filter_id'];
+        prevBatch = account['prev_batch'];
+        olmAccount = account['olm_account'];
       }
       if (newToken != null) {
-        accessToken = newToken;
+        accessToken = this.accessToken = newToken;
         homeserver = newHomeserver;
-        _userID = newUserID;
+        _userID = this._userID = newUserID;
         _deviceID = newDeviceID;
         _deviceName = newDeviceName;
         olmAccount = newOlmAccount;
       } else {
-        accessToken = newToken ?? accessToken;
+        accessToken = this.accessToken = newToken ?? accessToken;
         homeserver = newHomeserver ?? homeserver;
-        _userID = newUserID ?? _userID;
+        _userID = this._userID = newUserID ?? _userID;
         _deviceID = newDeviceID ?? _deviceID;
         _deviceName = newDeviceName ?? _deviceName;
         olmAccount = newOlmAccount ?? olmAccount;
@@ -970,6 +983,7 @@ class Client extends MatrixApi {
       }
       await encryption?.init(olmAccount);
 
+      final database = this.database;
       if (database != null) {
         if (id != null) {
           await database.updateClient(
@@ -1002,7 +1016,7 @@ class Client extends MatrixApi {
       _initLock = false;
       _loginState = LoginState.loggedIn;
       Logs().i(
-        'Successfully connected as ${userID.localpart} with ${homeserver.toString()}',
+        'Successfully connected as ${userID?.localpart} with ${homeserver.toString()}',
       );
 
       final syncFuture = _sync();
@@ -1042,6 +1056,7 @@ class Client extends MatrixApi {
     _rooms = [];
     encryption?.dispose();
     encryption = null;
+    final databaseDestroyer = this.databaseDestroyer;
     if (databaseDestroyer != null) {
       try {
         await database?.close();
@@ -1055,7 +1070,8 @@ class Client extends MatrixApi {
   }
 
   bool _backgroundSync = true;
-  Future<void> _currentSync, _retryDelay = Future.value();
+  Future<void>? _currentSync;
+  Future<void> _retryDelay = Future.value();
 
   bool get syncPending => _currentSync != null;
 
@@ -1073,25 +1089,28 @@ class Client extends MatrixApi {
     return _sync();
   }
 
-  Future<void> _sync() {
+  Future<void> _sync() async {
     if (_currentSync == null) {
-      _currentSync = _innerSync();
+      final _currentSync = this._currentSync = _innerSync();
+      // ignore: unawaited_futures
       _currentSync.whenComplete(() {
-        _currentSync = null;
+        this._currentSync = null;
         if (_backgroundSync && isLogged() && !_disposed) {
           _sync();
         }
       });
     }
-    return _currentSync;
+    await _currentSync;
   }
 
   /// Presence that is set on sync.
-  PresenceType syncPresence;
+  PresenceType? syncPresence;
 
   Future<void> _checkSyncFilter() async {
-    if (syncFilterId == null) {
-      syncFilterId = await defineFilter(userID, syncFilter);
+    final userID = this.userID;
+    if (syncFilterId == null && userID != null) {
+      final syncFilterId =
+          this.syncFilterId = await defineFilter(userID, syncFilter);
       await database?.storeSyncFilterId(syncFilterId);
     }
     return;
@@ -1113,7 +1132,7 @@ class Client extends MatrixApi {
         since: prevBatch,
         timeout: prevBatch != null ? 30000 : null,
         setPresence: syncPresence,
-      ).catchError((e) {
+      ).then((v) => Future<SyncUpdate?>.value(v)).catchError((e) {
         syncError = e;
         return null;
       });
@@ -1127,6 +1146,8 @@ class Client extends MatrixApi {
             .w('Current sync request ID has changed. Dropping this sync loop!');
         return;
       }
+
+      final database = this.database;
       if (database != null) {
         _currentTransaction = database.transaction(() async {
           await _handleSync(syncResp);
@@ -1151,7 +1172,7 @@ class Client extends MatrixApi {
           DateTime.now().subtract(Duration(days: 30)).millisecondsSinceEpoch);
       await updateUserDeviceKeys();
       if (encryptionEnabled) {
-        encryption.onSync();
+        encryption?.onSync();
       }
 
       // try to process the to_device queue
@@ -1189,47 +1210,45 @@ class Client extends MatrixApi {
   }
 
   Future<void> _handleSync(SyncUpdate sync, {bool sortAtTheEnd = false}) async {
-    if (sync.toDevice != null) {
-      await _handleToDeviceEvents(sync.toDevice);
+    final syncToDevice = sync.toDevice;
+    if (syncToDevice != null) {
+      await _handleToDeviceEvents(syncToDevice);
     }
+
     if (sync.rooms != null) {
-      if (sync.rooms.join != null) {
-        await _handleRooms(sync.rooms.join, Membership.join,
-            sortAtTheEnd: sortAtTheEnd);
+      final join = sync.rooms?.join;
+      if (join != null) {
+        await _handleRooms(join, sortAtTheEnd: sortAtTheEnd);
       }
-      if (sync.rooms.invite != null) {
-        await _handleRooms(sync.rooms.invite, Membership.invite,
-            sortAtTheEnd: sortAtTheEnd);
+      final invite = sync.rooms?.invite;
+      if (invite != null) {
+        await _handleRooms(invite, sortAtTheEnd: sortAtTheEnd);
       }
-      if (sync.rooms.leave != null) {
-        await _handleRooms(sync.rooms.leave, Membership.leave,
-            sortAtTheEnd: sortAtTheEnd);
+      final leave = sync.rooms?.leave;
+      if (leave != null) {
+        await _handleRooms(leave, sortAtTheEnd: sortAtTheEnd);
       }
       _sortRooms();
     }
-    if (sync.presence != null) {
-      for (final newPresence in sync.presence) {
-        presences[newPresence.senderId] = newPresence;
-        onPresence.add(newPresence);
-      }
+    for (final newPresence in sync.presence ?? []) {
+      presences[newPresence.senderId] = newPresence;
+      onPresence.add(newPresence);
     }
-    if (sync.accountData != null) {
-      for (final newAccountData in sync.accountData) {
-        if (database != null) {
-          await database.storeAccountData(
-            newAccountData.type,
-            jsonEncode(newAccountData.content),
-          );
-        }
-        accountData[newAccountData.type] = newAccountData;
-        if (onAccountData != null) onAccountData.add(newAccountData);
-      }
+    for (final newAccountData in sync.accountData ?? []) {
+      await database?.storeAccountData(
+        newAccountData.type,
+        jsonEncode(newAccountData.content),
+      );
+      accountData[newAccountData.type] = newAccountData;
+      onAccountData.add(newAccountData);
     }
-    if (sync.deviceLists != null) {
-      await _handleDeviceListsEvents(sync.deviceLists);
+
+    final syncDeviceLists = sync.deviceLists;
+    if (syncDeviceLists != null) {
+      await _handleDeviceListsEvents(syncDeviceLists);
     }
     if (encryptionEnabled) {
-      encryption.handleDeviceOneTimeKeysCount(
+      encryption?.handleDeviceOneTimeKeysCount(
           sync.deviceOneTimeKeysCount, sync.deviceUnusedFallbackKeyTypes);
     }
     onSync.add(sync);
@@ -1237,15 +1256,14 @@ class Client extends MatrixApi {
 
   Future<void> _handleDeviceListsEvents(DeviceListsUpdate deviceLists) async {
     if (deviceLists.changed is List) {
-      for (final userId in deviceLists.changed) {
-        if (_userDeviceKeys.containsKey(userId)) {
-          _userDeviceKeys[userId].outdated = true;
-          if (database != null) {
-            await database.storeUserDeviceKeysInfo(userId, true);
-          }
+      for (final userId in deviceLists.changed ?? []) {
+        final userKeys = _userDeviceKeys[userId];
+        if (userKeys != null) {
+          userKeys.outdated = true;
+          await database?.storeUserDeviceKeysInfo(userId, true);
         }
       }
-      for (final userId in deviceLists.left) {
+      for (final userId in deviceLists.left ?? []) {
         if (_userDeviceKeys.containsKey(userId)) {
           _userDeviceKeys.remove(userId);
         }
@@ -1258,18 +1276,17 @@ class Client extends MatrixApi {
       var toDeviceEvent = ToDeviceEvent.fromJson(event.toJson());
       Logs().v('Got to_device event of type ${toDeviceEvent.type}');
       if (toDeviceEvent.type == EventTypes.Encrypted && encryptionEnabled) {
-        toDeviceEvent = await encryption.decryptToDeviceEvent(toDeviceEvent);
+        toDeviceEvent = await encryption!.decryptToDeviceEvent(toDeviceEvent);
         Logs().v('Decrypted type is: ${toDeviceEvent.type}');
       }
       if (encryptionEnabled) {
-        await encryption.handleToDeviceEvent(toDeviceEvent);
+        await encryption?.handleToDeviceEvent(toDeviceEvent);
       }
       onToDeviceEvent.add(toDeviceEvent);
     }
   }
 
-  Future<void> _handleRooms(
-      Map<String, SyncRoomUpdate> rooms, Membership membership,
+  Future<void> _handleRooms(Map<String, SyncRoomUpdate> rooms,
       {bool sortAtTheEnd = false}) async {
     var handledRooms = 0;
     for (final entry in rooms.entries) {
@@ -1280,67 +1297,73 @@ class Client extends MatrixApi {
       final id = entry.key;
       final room = entry.value;
 
-      if (database != null) {
-        // TODO: This method seems to be rather slow for some updates
-        // Perhaps don't dynamically build that one query?
-        await database.storeRoomUpdate(id, room, getRoomById(id));
-      }
+      await database?.storeRoomUpdate(id, room);
       _updateRoomsByRoomUpdate(id, room);
 
       /// Handle now all room events and save them in the database
       if (room is JoinedRoomUpdate) {
-        if (room.state?.isNotEmpty ?? false) {
+        final state = room.state;
+        if (state != null && state.isNotEmpty) {
           // TODO: This method seems to be comperatively slow for some updates
-          await _handleRoomEvents(id,
-              room.state.map((i) => i.toJson()).toList(), EventUpdateType.state,
+          await _handleRoomEvents(
+              id, state.map((i) => i.toJson()).toList(), EventUpdateType.state,
               sortAtTheEnd: sortAtTheEnd);
         }
-        if (room.timeline?.events?.isNotEmpty ?? false) {
+
+        final timelineEvents = room.timeline?.events;
+        if (timelineEvents != null && timelineEvents.isNotEmpty) {
           await _handleRoomEvents(
               id,
-              room.timeline.events.map((i) => i.toJson()).toList(),
+              timelineEvents.map((i) => i.toJson()).toList(),
               sortAtTheEnd ? EventUpdateType.history : EventUpdateType.timeline,
               sortAtTheEnd: sortAtTheEnd);
         }
-        if (room.ephemeral?.isNotEmpty ?? false) {
+
+        final ephemeral = room.ephemeral;
+        if (ephemeral != null && ephemeral.isNotEmpty) {
           // TODO: This method seems to be comperatively slow for some updates
           await _handleEphemerals(
-              id, room.ephemeral.map((i) => i.toJson()).toList());
+              id, ephemeral.map((i) => i.toJson()).toList());
         }
-        if (room.accountData?.isNotEmpty ?? false) {
+
+        final accountData = room.accountData;
+        if (accountData != null && accountData.isNotEmpty) {
           await _handleRoomEvents(
               id,
-              room.accountData.map((i) => i.toJson()).toList(),
+              accountData.map((i) => i.toJson()).toList(),
               EventUpdateType.accountData);
         }
       }
+
       if (room is LeftRoomUpdate) {
-        if (room.timeline?.events?.isNotEmpty ?? false) {
+        final timelineEvents = room.timeline?.events;
+        if (timelineEvents != null && timelineEvents.isNotEmpty) {
           await _handleRoomEvents(
               id,
-              room.timeline.events.map((i) => i.toJson()).toList(),
+              timelineEvents.map((i) => i.toJson()).toList(),
               EventUpdateType.timeline,
               sortAtTheEnd: sortAtTheEnd);
         }
-        if (room.accountData?.isNotEmpty ?? false) {
+        final accountData = room.accountData;
+        if (accountData != null && accountData.isNotEmpty) {
           await _handleRoomEvents(
               id,
-              room.accountData.map((i) => i.toJson()).toList(),
+              accountData.map((i) => i.toJson()).toList(),
               EventUpdateType.accountData);
         }
-        if (room.state?.isNotEmpty ?? false) {
+        final state = room.state;
+        if (state != null && state.isNotEmpty) {
           await _handleRoomEvents(
-              id,
-              room.state.map((i) => i.toJson()).toList(),
-              EventUpdateType.state);
+              id, state.map((i) => i.toJson()).toList(), EventUpdateType.state);
         }
       }
-      if (room is InvitedRoomUpdate &&
-          (room.inviteState?.isNotEmpty ?? false)) {
-        await _handleRoomEvents(
-            id,
-            room.inviteState.map((i) => i.toJson()).toList(),
-            EventUpdateType.inviteState);
+
+      if (room is InvitedRoomUpdate) {
+        final state = room.inviteState;
+        if (state != null && state.isNotEmpty) {
+          await _handleRoomEvents(id, state.map((i) => i.toJson()).toList(),
+              EventUpdateType.inviteState);
+        }
       }
     }
   }
@@ -1425,17 +1448,17 @@ class Client extends MatrixApi {
           database != null &&
           room.getState(EventTypes.RoomMember, event['sender']) == null) {
         // In order to correctly render room list previews we need to fetch the member from the database
-        final user = await database.getUser(event['sender'], room);
+        final user = await database?.getUser(event['sender'], room);
         if (user != null) {
           room.setState(user);
         }
       }
       _updateRoomsByEventUpdate(update);
-      if (type != EventUpdateType.ephemeral && database != null) {
-        await database.storeEventUpdate(update);
+      if (type != EventUpdateType.ephemeral) {
+        await database?.storeEventUpdate(update);
       }
       if (encryptionEnabled) {
-        await encryption.handleEventUpdate(update);
+        await encryption?.handleEventUpdate(update);
       }
       onEvent.add(update);
 
@@ -1478,7 +1501,7 @@ class Client extends MatrixApi {
   void _updateRoomsByRoomUpdate(String roomId, SyncRoomUpdate chatUpdate) {
     // Update the chat list item.
     // Search the room in the rooms
-    num j = 0;
+    var j = 0;
     for (j = 0; j < rooms.length; j++) {
       if (rooms[j].id == roomId) break;
     }
@@ -1529,13 +1552,15 @@ class Client extends MatrixApi {
       if (chatUpdate.timeline?.prevBatch != null) {
         rooms[j].prev_batch = chatUpdate.timeline?.prevBatch;
       }
-      if (chatUpdate.summary != null) {
+
+      final summary = chatUpdate.summary;
+      if (summary != null) {
         final roomSummaryJson = rooms[j].summary.toJson()
-          ..addAll(chatUpdate.summary.toJson());
+          ..addAll(summary.toJson());
         rooms[j].summary = RoomSummary.fromJson(roomSummaryJson);
       }
       if (rooms[j].onUpdate != null) rooms[j].onUpdate.add(rooms[j].id);
-      if ((chatUpdate?.timeline?.limited ?? false) &&
+      if ((chatUpdate.timeline?.limited ?? false) &&
           requestHistoryOnLimitedTimeline) {
         Logs().v('Limited timeline for ${rooms[j].id} request history now');
         runInRoot(rooms[j].requestHistory);
@@ -1620,10 +1645,10 @@ class Client extends MatrixApi {
   Map<String, DeviceKeysList> _userDeviceKeys = {};
 
   /// Gets user device keys by its curve25519 key. Returns null if it isn't found
-  DeviceKeys getUserDeviceKeysByCurve25519Key(String senderKey) {
+  DeviceKeys? getUserDeviceKeysByCurve25519Key(String senderKey) {
     for (final user in userDeviceKeys.values) {
       final device = user.deviceKeys.values
-          .firstWhere((e) => e.curve25519Key == senderKey, orElse: () => null);
+          .firstWhereOrNull((e) => e.curve25519Key == senderKey);
       if (device != null) {
         return device;
       }
@@ -1655,11 +1680,12 @@ class Client extends MatrixApi {
 
   Future<void> updateUserDeviceKeys() async {
     try {
+      final database = this.database;
       if (!isLogged() || database == null) return;
       final dbActions = <Future<dynamic> Function()>[];
       final trackedUserIds = await _getUserIdsInEncryptedRooms();
       if (!isLogged()) return;
-      trackedUserIds.add(userID);
+      trackedUserIds.add(userID!);
 
       // Remove all userIds we no longer need to track the devices of.
       _userDeviceKeys
@@ -1668,15 +1694,14 @@ class Client extends MatrixApi {
       // Check if there are outdated device key lists. Add it to the set.
       final outdatedLists = <String, List<String>>{};
       for (final userId in trackedUserIds) {
-        if (!userDeviceKeys.containsKey(userId)) {
-          _userDeviceKeys[userId] = DeviceKeysList(userId, this);
-        }
-        final deviceKeysList = userDeviceKeys[userId];
+        final deviceKeysList =
+            _userDeviceKeys[userId] ??= DeviceKeysList(userId, this);
+        final failure = _keyQueryFailures[userId.domain];
         if (deviceKeysList.outdated &&
-            (!_keyQueryFailures.containsKey(userId.domain) ||
+            (failure == null ||
                 DateTime.now()
                     .subtract(Duration(minutes: 5))
-                    .isAfter(_keyQueryFailures[userId.domain]))) {
+                    .isAfter(failure))) {
           outdatedLists[userId] = [];
         }
       }
@@ -1686,15 +1711,14 @@ class Client extends MatrixApi {
         final response = await queryKeys(outdatedLists, timeout: 10000);
         if (!isLogged()) return;
 
-        if (response.deviceKeys != null) {
-          for (final rawDeviceKeyListEntry in response.deviceKeys.entries) {
+        final deviceKeys = response.deviceKeys;
+        if (deviceKeys != null) {
+          for (final rawDeviceKeyListEntry in deviceKeys.entries) {
             final userId = rawDeviceKeyListEntry.key;
-            if (!userDeviceKeys.containsKey(userId)) {
-              _userDeviceKeys[userId] = DeviceKeysList(userId, this);
-            }
-            final oldKeys = Map<String, DeviceKeys>.from(
-                _userDeviceKeys[userId].deviceKeys);
-            _userDeviceKeys[userId].deviceKeys = {};
+            final userKeys =
+                _userDeviceKeys[userId] ??= DeviceKeysList(userId, this);
+            final oldKeys = Map<String, DeviceKeys>.from(userKeys.deviceKeys);
+            userKeys.deviceKeys = {};
             for (final rawDeviceKeyEntry
                 in rawDeviceKeyListEntry.value.entries) {
               final deviceId = rawDeviceKeyEntry.key;
@@ -1702,51 +1726,54 @@ class Client extends MatrixApi {
               // Set the new device key for this device
               final entry = DeviceKeys.fromMatrixDeviceKeys(
                   rawDeviceKeyEntry.value, this, oldKeys[deviceId]?.lastActive);
-              if (entry.isValid && deviceId == entry.deviceId) {
+              final ed25519Key = entry.ed25519Key;
+              final curve25519Key = entry.curve25519Key;
+              if (entry.isValid &&
+                  deviceId == entry.deviceId &&
+                  ed25519Key != null &&
+                  curve25519Key != null) {
                 // Check if deviceId or deviceKeys are known
                 if (!oldKeys.containsKey(deviceId)) {
                   final oldPublicKeys =
                       await database.deviceIdSeen(userId, deviceId);
                   if (oldPublicKeys != null &&
-                      oldPublicKeys != entry.curve25519Key + entry.ed25519Key) {
+                      oldPublicKeys != curve25519Key + ed25519Key) {
                     Logs().w(
                         'Already seen Device ID has been added again. This might be an attack!');
                     continue;
                   }
-                  final oldDeviceId =
-                      await database.publicKeySeen(entry.ed25519Key);
+                  final oldDeviceId = await database.publicKeySeen(ed25519Key);
                   if (oldDeviceId != null && oldDeviceId != deviceId) {
                     Logs().w(
                         'Already seen ED25519 has been added again. This might be an attack!');
                     continue;
                   }
                   final oldDeviceId2 =
-                      await database.publicKeySeen(entry.curve25519Key);
+                      await database.publicKeySeen(curve25519Key);
                   if (oldDeviceId2 != null && oldDeviceId2 != deviceId) {
                     Logs().w(
                         'Already seen Curve25519 has been added again. This might be an attack!');
                     continue;
                   }
                   await database.addSeenDeviceId(
-                      userId, deviceId, entry.curve25519Key + entry.ed25519Key);
-                  await database.addSeenPublicKey(entry.ed25519Key, deviceId);
-                  await database.addSeenPublicKey(
-                      entry.curve25519Key, deviceId);
+                      userId, deviceId, curve25519Key + ed25519Key);
+                  await database.addSeenPublicKey(ed25519Key, deviceId);
+                  await database.addSeenPublicKey(curve25519Key, deviceId);
                 }
 
                 // is this a new key or the same one as an old one?
                 // better store an update - the signatures might have changed!
-                if (!oldKeys.containsKey(deviceId) ||
-                    (oldKeys[deviceId].ed25519Key == entry.ed25519Key &&
-                        oldKeys[deviceId].curve25519Key ==
-                            entry.curve25519Key)) {
-                  if (oldKeys.containsKey(deviceId)) {
+                final oldKey = oldKeys[deviceId];
+                if (oldKey == null ||
+                    (oldKey.ed25519Key == entry.ed25519Key &&
+                        oldKey.curve25519Key == entry.curve25519Key)) {
+                  if (oldKey != null) {
                     // be sure to save the verified status
-                    entry.setDirectVerified(oldKeys[deviceId].directVerified);
-                    entry.blocked = oldKeys[deviceId].blocked;
-                    entry.validSignatures = oldKeys[deviceId].validSignatures;
+                    entry.setDirectVerified(oldKey.directVerified);
+                    entry.blocked = oldKey.blocked;
+                    entry.validSignatures = oldKey.validSignatures;
                   }
-                  _userDeviceKeys[userId].deviceKeys[deviceId] = entry;
+                  userKeys.deviceKeys[deviceId] = entry;
                   if (deviceId == deviceID &&
                       entry.ed25519Key == fingerprintKey) {
                     // Always trust the own device
@@ -1764,8 +1791,7 @@ class Client extends MatrixApi {
                   // This shouldn't ever happen. The same device ID has gotten
                   // a new public key. So we ignore the update. TODO: ask krille
                   // if we should instead use the new key with unknown verified / blocked status
-                  _userDeviceKeys[userId].deviceKeys[deviceId] =
-                      oldKeys[deviceId];
+                  userKeys.deviceKeys[deviceId] = oldKeys[deviceId]!;
                 }
               } else {
                 Logs().w('Invalid device ${entry.userId}:${entry.deviceId}');
@@ -1774,13 +1800,13 @@ class Client extends MatrixApi {
             // delete old/unused entries
             for (final oldDeviceKeyEntry in oldKeys.entries) {
               final deviceId = oldDeviceKeyEntry.key;
-              if (!_userDeviceKeys[userId].deviceKeys.containsKey(deviceId)) {
+              if (!userKeys.deviceKeys.containsKey(deviceId)) {
                 // we need to remove an old key
                 dbActions
                     .add(() => database.removeUserDeviceKey(userId, deviceId));
               }
             }
-            _userDeviceKeys[userId].outdated = false;
+            userKeys.outdated = false;
             if (database != null) {
               dbActions
                   .add(() => database.storeUserDeviceKeysInfo(userId, false));
@@ -1801,17 +1827,15 @@ class Client extends MatrixApi {
           }
           for (final crossSigningKeyListEntry in keys.entries) {
             final userId = crossSigningKeyListEntry.key;
-            if (!userDeviceKeys.containsKey(userId)) {
-              _userDeviceKeys[userId] = DeviceKeysList(userId, this);
-            }
-            final oldKeys = Map<String, CrossSigningKey>.from(
-                _userDeviceKeys[userId].crossSigningKeys);
-            _userDeviceKeys[userId].crossSigningKeys = {};
+            final userKeys =
+                _userDeviceKeys[userId] ??= DeviceKeysList(userId, this);
+            final oldKeys =
+                Map<String, CrossSigningKey>.from(userKeys.crossSigningKeys);
+            userKeys.crossSigningKeys = {};
             // add the types we aren't handling atm back
             for (final oldEntry in oldKeys.entries) {
               if (!oldEntry.value.usage.contains(keyType)) {
-                _userDeviceKeys[userId].crossSigningKeys[oldEntry.key] =
-                    oldEntry.value;
+                userKeys.crossSigningKeys[oldEntry.key] = oldEntry.value;
               } else if (database != null) {
                 // There is a previous cross-signing key with  this usage, that we no
                 // longer need/use. Clear it from the database.
@@ -1821,23 +1845,22 @@ class Client extends MatrixApi {
             }
             final entry = CrossSigningKey.fromMatrixCrossSigningKey(
                 crossSigningKeyListEntry.value, this);
-            if (entry.isValid) {
-              final publicKey = entry.publicKey;
-              if (!oldKeys.containsKey(publicKey) ||
-                  oldKeys[publicKey].ed25519Key == entry.ed25519Key) {
-                if (oldKeys.containsKey(publicKey)) {
+            final publicKey = entry.publicKey;
+            if (entry.isValid && publicKey != null) {
+              final oldKey = oldKeys[publicKey];
+              if (oldKey == null || oldKey.ed25519Key == entry.ed25519Key) {
+                if (oldKey != null) {
                   // be sure to save the verification status
-                  entry.setDirectVerified(oldKeys[publicKey].directVerified);
-                  entry.blocked = oldKeys[publicKey].blocked;
-                  entry.validSignatures = oldKeys[publicKey].validSignatures;
+                  entry.setDirectVerified(oldKey.directVerified);
+                  entry.blocked = oldKey.blocked;
+                  entry.validSignatures = oldKey.validSignatures;
                 }
-                _userDeviceKeys[userId].crossSigningKeys[publicKey] = entry;
+                userKeys.crossSigningKeys[publicKey] = entry;
               } else {
                 // This shouldn't ever happen. The same device ID has gotten
                 // a new public key. So we ignore the update. TODO: ask krille
                 // if we should instead use the new key with unknown verified / blocked status
-                _userDeviceKeys[userId].crossSigningKeys[publicKey] =
-                    oldKeys[publicKey];
+                userKeys.crossSigningKeys[publicKey] = oldKey;
               }
               if (database != null) {
                 dbActions.add(() => database.storeUserCrossSigningKey(
@@ -1849,7 +1872,7 @@ class Client extends MatrixApi {
                     ));
               }
             }
-            _userDeviceKeys[userId].outdated = false;
+            _userDeviceKeys[userId]?.outdated = false;
             if (database != null) {
               dbActions
                   .add(() => database.storeUserDeviceKeysInfo(userId, false));
@@ -1859,7 +1882,7 @@ class Client extends MatrixApi {
 
         // now process all the failures
         if (response.failures != null) {
-          for (final failureDomain in response.failures.keys) {
+          for (final failureDomain in response.failures?.keys ?? <String>[]) {
             _keyQueryFailures[failureDomain] = DateTime.now();
           }
         }
@@ -1867,7 +1890,7 @@ class Client extends MatrixApi {
 
       if (dbActions.isNotEmpty) {
         if (!isLogged()) return;
-        await database?.transaction(() async {
+        await database.transaction(() async {
           for (final f in dbActions) {
             await f();
           }
@@ -1884,6 +1907,7 @@ class Client extends MatrixApi {
   /// This function MAY throw an error, which just means the to_device queue wasn't
   /// proccessed all the way.
   Future<void> processToDeviceQueue() async {
+    final database = this.database;
     if (database == null || !_toDeviceQueueNeedsProcessing) {
       return;
     }
@@ -1923,6 +1947,7 @@ class Client extends MatrixApi {
           '[Client] Problem while sending to_device event, retrying later...',
           e,
           s);
+      final database = this.database;
       if (database != null) {
         _toDeviceQueueNeedsProcessing = true;
         await database.insertIntoToDeviceQueue(
@@ -1938,13 +1963,12 @@ class Client extends MatrixApi {
     Set<String> users,
     String eventType,
     Map<String, dynamic> message, {
-    String messageId,
+    String? messageId,
   }) async {
     // Send with send-to-device messaging
     final data = <String, Map<String, Map<String, dynamic>>>{};
     for (final user in users) {
-      data[user] = {};
-      data[user]['*'] = message;
+      data[user] = {'*': message};
     }
     await sendToDevice(
         eventType, messageId ?? generateUniqueTransactionId(), data);
@@ -1958,10 +1982,11 @@ class Client extends MatrixApi {
     List<DeviceKeys> deviceKeys,
     String eventType,
     Map<String, dynamic> message, {
-    String messageId,
+    String? messageId,
     bool onlyVerified = false,
   }) async {
-    if (!encryptionEnabled) return;
+    final encryption = this.encryption;
+    if (!encryptionEnabled || encryption == null) return;
     // Don't send this message to blocked devices, and if specified onlyVerified
     // then only send it to verified devices
     if (deviceKeys.isNotEmpty) {
@@ -1985,9 +2010,9 @@ class Client extends MatrixApi {
       await _sendToDeviceEncryptedLock.lock(deviceKeys);
 
       // Send with send-to-device messaging
-      var data = <String, Map<String, Map<String, dynamic>>>{};
-      data = await encryption.encryptToDeviceMessage(
-          deviceKeys, eventType, message);
+      final data = await encryption.encryptToDeviceMessage(
+              deviceKeys, eventType, message)
+          as Map<String, Map<String, Map<String, dynamic>>>;
       eventType = EventTypes.Encrypted;
       await sendToDevice(
           eventType, messageId ?? generateUniqueTransactionId(), data);
@@ -2057,12 +2082,8 @@ class Client extends MatrixApi {
   /// Whether all push notifications are muted using the [.m.rule.master]
   /// rule of the push rules: https://matrix.org/docs/spec/client_server/r0.6.0#m-rule-master
   bool get allPushNotificationsMuted {
-    if (!accountData.containsKey('m.push_rules') ||
-        !(accountData['m.push_rules'].content['global'] is Map)) {
-      return false;
-    }
-    final Map<String, dynamic> globalPushRules =
-        accountData['m.push_rules'].content['global'];
+    final Map<String, dynamic>? globalPushRules =
+        accountData['m.push_rules']?.content['global'];
     if (globalPushRules == null) return false;
 
     if (globalPushRules['override'] is List) {
@@ -2088,7 +2109,11 @@ class Client extends MatrixApi {
   /// Changes the password. You should either set oldPasswort or another authentication flow.
   @override
   Future<void> changePassword(String newPassword,
-      {String oldPassword, AuthenticationData auth, bool logoutDevices}) async {
+      {String? oldPassword,
+      AuthenticationData? auth,
+      bool? logoutDevices}) async {
+    final userID = this.userID;
+    if (userID == null) return;
     try {
       if (oldPassword != null) {
         auth = AuthenticationPassword(
@@ -2102,9 +2127,10 @@ class Client extends MatrixApi {
       if (!matrixException.requireAdditionalAuthentication) {
         rethrow;
       }
-      if (matrixException.authenticationFlows.length != 1 ||
-          !matrixException.authenticationFlows.first.stages
-              .contains(AuthenticationTypes.password)) {
+      if (matrixException.authenticationFlows?.length != 1 ||
+          !(matrixException.authenticationFlows?.first.stages
+                  .contains(AuthenticationTypes.password) ??
+              false)) {
         rethrow;
       }
       if (oldPassword == null) {
@@ -2136,7 +2162,7 @@ class Client extends MatrixApi {
     prevBatch = null;
     rooms.clear();
     await database?.clearCache();
-    encryption?.keyManager?.clearOutboundGroupSessions();
+    encryption?.keyManager.clearOutboundGroupSessions();
     onCacheCleared.add(true);
     // Restart the syncloop
     backgroundSync = true;
@@ -2145,9 +2171,9 @@ class Client extends MatrixApi {
   /// A list of mxids of users who are ignored.
   List<String> get ignoredUsers => (accountData
               .containsKey('m.ignored_user_list') &&
-          accountData['m.ignored_user_list'].content['ignored_users'] is Map)
+          accountData['m.ignored_user_list']?.content['ignored_users'] is Map)
       ? List<String>.from(
-          accountData['m.ignored_user_list'].content['ignored_users'].keys)
+          accountData['m.ignored_user_list']?.content['ignored_users'].keys)
       : [];
 
   /// Ignore another user. This will clear the local cached messages to
@@ -2156,7 +2182,7 @@ class Client extends MatrixApi {
     if (!userId.isValidMatrixId) {
       throw Exception('$userId is not a valid mxid!');
     }
-    await setAccountData(userID, 'm.ignored_user_list', {
+    await setAccountData(userID!, 'm.ignored_user_list', {
       'ignored_users': Map.fromEntries(
           (ignoredUsers..add(userId)).map((key) => MapEntry(key, {}))),
     });
@@ -2173,7 +2199,7 @@ class Client extends MatrixApi {
     if (!ignoredUsers.contains(userId)) {
       throw Exception('$userId is not in the ignore list!');
     }
-    await setAccountData(userID, 'm.ignored_user_list', {
+    await setAccountData(userID!, 'm.ignored_user_list', {
       'ignored_users': Map.fromEntries(
           (ignoredUsers..remove(userId)).map((key) => MapEntry(key, {}))),
     });
@@ -2209,9 +2235,9 @@ class Client extends MatrixApi {
     encryption?.dispose();
     encryption = null;
     try {
-      if (closeDatabase && database != null) {
+      if (closeDatabase) {
         await database
-            .close()
+            ?.close()
             .catchError((e, s) => Logs().w('Failed to close database: ', e, s));
         _database = null;
       }
@@ -2223,10 +2249,11 @@ class Client extends MatrixApi {
 
   Future<void> _migrateFromLegacyDatabase() async {
     Logs().i('Check legacy database for migration data...');
-    final legacyDatabase = await legacyDatabaseBuilder(this);
-    final migrateClient = await legacyDatabase.getClient(clientName);
+    final legacyDatabase = await legacyDatabaseBuilder?.call(this);
+    final migrateClient = await legacyDatabase?.getClient(clientName);
+    final database = this.database;
 
-    if (migrateClient != null) {
+    if (migrateClient != null && legacyDatabase != null && database != null) {
       Logs().i('Found data in the legacy database!');
       _id = migrateClient['client_id'];
       await database.insertClient(
@@ -2246,9 +2273,9 @@ class Client extends MatrixApi {
           Logs().d('Migrate $type...');
           await database.storeSSSSCache(
             type,
-            ssssCache.keyId,
-            ssssCache.ciphertext,
-            ssssCache.content,
+            ssssCache.keyId ?? '',
+            ssssCache.ciphertext ?? '',
+            ssssCache.content ?? '',
           );
         }
       }
@@ -2257,30 +2284,41 @@ class Client extends MatrixApi {
       for (final userId in userDeviceKeys.keys) {
         Logs().d('Migrate Device Keys of user $userId...');
         final deviceKeysList = userDeviceKeys[userId];
-        for (final crossSigningKey in deviceKeysList.crossSigningKeys.values) {
-          Logs().d(
-              'Migrate cross signing key with usage ${crossSigningKey.usage} and verified ${crossSigningKey.directVerified}...');
-          await database.storeUserCrossSigningKey(
-            userId,
-            crossSigningKey.publicKey,
-            jsonEncode(crossSigningKey.toJson()),
-            crossSigningKey.directVerified,
-            crossSigningKey.blocked,
-          );
+        for (final crossSigningKey
+            in deviceKeysList?.crossSigningKeys.values ?? <CrossSigningKey>[]) {
+          final pubKey = crossSigningKey.publicKey;
+          if (pubKey != null) {
+            Logs().d(
+                'Migrate cross signing key with usage ${crossSigningKey.usage} and verified ${crossSigningKey.directVerified}...');
+            await database.storeUserCrossSigningKey(
+              userId,
+              pubKey,
+              jsonEncode(crossSigningKey.toJson()),
+              crossSigningKey.directVerified,
+              crossSigningKey.blocked,
+            );
+          }
         }
-        for (final deviceKeys in deviceKeysList.deviceKeys.values) {
-          Logs().d('Migrate device keys for ${deviceKeys.deviceId}...');
-          await database.storeUserDeviceKey(
-            userId,
-            deviceKeys.deviceId,
-            jsonEncode(deviceKeys.toJson()),
-            deviceKeys.directVerified,
-            deviceKeys.blocked,
-            deviceKeys.lastActive.millisecondsSinceEpoch,
-          );
+
+        if (deviceKeysList != null) {
+          for (final deviceKeys in deviceKeysList.deviceKeys.values) {
+            final deviceId = deviceKeys.deviceId;
+            if (deviceId != null) {
+              Logs().d('Migrate device keys for ${deviceKeys.deviceId}...');
+              await database.storeUserDeviceKey(
+                userId,
+                deviceId,
+                jsonEncode(deviceKeys.toJson()),
+                deviceKeys.directVerified,
+                deviceKeys.blocked,
+                deviceKeys.lastActive.millisecondsSinceEpoch,
+              );
+            }
+          }
+          Logs().d('Migrate user device keys info...');
+          await database.storeUserDeviceKeysInfo(
+              userId, deviceKeysList.outdated);
         }
-        Logs().d('Migrate user device keys info...');
-        await database.storeUserDeviceKeysInfo(userId, deviceKeysList.outdated);
       }
       Logs().d('Migrate inbound group sessions...');
       try {
@@ -2306,7 +2344,7 @@ class Client extends MatrixApi {
       await legacyDatabase.clear();
       await legacyDatabaseDestroyer?.call(this);
     }
-    await legacyDatabase.close();
+    await legacyDatabase?.close();
     _initLock = false;
     if (migrateClient != null) {
       return init();
@@ -2316,15 +2354,15 @@ class Client extends MatrixApi {
 
 class SdkError {
   dynamic exception;
-  StackTrace stackTrace;
+  StackTrace? stackTrace;
 
   SdkError({this.exception, this.stackTrace});
 }
 
 class SyncStatusUpdate {
   final SyncStatus status;
-  final SdkError error;
-  final double progress;
+  final SdkError? error;
+  final double? progress;
   const SyncStatusUpdate(this.status, {this.error, this.progress});
 }
 
diff --git a/lib/src/database/database_api.dart b/lib/src/database/database_api.dart
index 9345d8f2..ca9ff333 100644
--- a/lib/src/database/database_api.dart
+++ b/lib/src/database/database_api.dart
@@ -35,10 +35,10 @@ abstract class DatabaseApi {
     String homeserverUrl,
     String token,
     String userId,
-    String deviceId,
-    String deviceName,
-    String prevBatch,
-    String olmAccount,
+    String? deviceId,
+    String? deviceName,
+    String? prevBatch,
+    String? olmAccount,
   );
 
   Future insertClient(
@@ -46,10 +46,10 @@ abstract class DatabaseApi {
     String homeserverUrl,
     String token,
     String userId,
-    String deviceId,
-    String deviceName,
-    String prevBatch,
-    String olmAccount,
+    String? deviceId,
+    String? deviceName,
+    String? prevBatch,
+    String? olmAccount,
   );
 
   Future<List<Room>> getRoomList(Client client);
@@ -58,8 +58,7 @@ abstract class DatabaseApi {
 
   /// Stores a RoomUpdate object in the database. Must be called inside of
   /// [transaction].
-  Future<void> storeRoomUpdate(String roomId, SyncRoomUpdate roomUpdate,
-      [Room oldRoom]);
+  Future<void> storeRoomUpdate(String roomId, SyncRoomUpdate roomUpdate);
 
   /// Stores an EventUpdate object in the database. Must be called inside of
   /// [transaction].
diff --git a/lib/src/database/hive_database.dart b/lib/src/database/hive_database.dart
index f9a4a1da..625f70f7 100644
--- a/lib/src/database/hive_database.dart
+++ b/lib/src/database/hive_database.dart
@@ -507,6 +507,7 @@ class FamedlySdkHiveDatabase extends DatabaseApi {
   Future<List<Room>> getRoomList(Client client) =>
       runBenchmarked<List<Room>>('Get room list from hive', () async {
         final rooms = <String, Room>{};
+        final userID = client.userID;
         final importantRoomStates = client.importantStateEvents;
         for (final key in _roomsBox.keys) {
           // Get the room
@@ -515,7 +516,7 @@ class FamedlySdkHiveDatabase extends DatabaseApi {
 
           // let's see if we need any m.room.member events
           // We always need the member event for ourself
-          final membersToPostload = <String>{client.userID};
+          final membersToPostload = <String>{if (userID != null) userID};
           // If the room is a direct chat, those IDs should be there too
           if (room.isDirectChat) membersToPostload.add(room.directChatMatrixID);
           // the lastEvent message preview might have an author we need to fetch, if it is a group chat
@@ -671,10 +672,10 @@ class FamedlySdkHiveDatabase extends DatabaseApi {
       String homeserverUrl,
       String token,
       String userId,
-      String deviceId,
-      String deviceName,
-      String prevBatch,
-      String olmAccount) async {
+      String? deviceId,
+      String? deviceName,
+      String? prevBatch,
+      String? olmAccount) async {
     await _clientBox.put('homeserver_url', homeserverUrl);
     await _clientBox.put('token', token);
     await _clientBox.put('user_id', userId);
@@ -1076,8 +1077,7 @@ class FamedlySdkHiveDatabase extends DatabaseApi {
   }
 
   @override
-  Future<void> storeRoomUpdate(String roomId, SyncRoomUpdate roomUpdate,
-      [dynamic _]) async {
+  Future<void> storeRoomUpdate(String roomId, SyncRoomUpdate roomUpdate) async {
     // Leave room if membership is leave
     if (roomUpdate is LeftRoomUpdate) {
       await forgetRoom(roomId);
@@ -1250,10 +1250,10 @@ class FamedlySdkHiveDatabase extends DatabaseApi {
     String homeserverUrl,
     String token,
     String userId,
-    String deviceId,
-    String deviceName,
-    String prevBatch,
-    String olmAccount,
+    String? deviceId,
+    String? deviceName,
+    String? prevBatch,
+    String? olmAccount,
   ) async {
     await _clientBox.put('homeserver_url', homeserverUrl);
     await _clientBox.put('token', token);
diff --git a/lib/src/event.dart b/lib/src/event.dart
index 2a21d9ad..94ed3d78 100644
--- a/lib/src/event.dart
+++ b/lib/src/event.dart
@@ -518,7 +518,7 @@ class Event extends MatrixEvent {
   /// event and returns it as a [MatrixFile]. If this event doesn't
   /// contain an attachment, this throws an error. Set [getThumbnail] to
   /// true to download the thumbnail instead.
-  Future<MatrixFile> downloadAndDecryptAttachment(
+  Future<MatrixFile?> downloadAndDecryptAttachment(
       {bool getThumbnail = false,
       Future<Uint8List> Function(Uri)? downloadCallback}) async {
     if (![EventTypes.Message, EventTypes.Sticker].contains(type)) {
@@ -548,7 +548,7 @@ class Event extends MatrixEvent {
 
     Uint8List? uint8list;
     if (storeable) {
-      uint8list = await client.database.getFile(mxcUrl);
+      uint8list = await client.database?.getFile(mxcUrl);
     }
 
     // Download the file
@@ -577,9 +577,10 @@ class Event extends MatrixEvent {
         k: fileMap['key']['k'],
         sha256: fileMap['hashes']['sha256'],
       );
-      uint8list = await client.runInBackground(decryptFile, encryptedFile);
+      uint8list = await client.runInBackground<Uint8List?, EncryptedFile>(
+          decryptFile, encryptedFile);
     }
-    return MatrixFile(bytes: uint8list, name: body);
+    return uint8list != null ? MatrixFile(bytes: uint8list, name: body) : null;
   }
 
   /// Returns if this is a known event type.
diff --git a/lib/src/timeline.dart b/lib/src/timeline.dart
index 9147bba6..1be71186 100644
--- a/lib/src/timeline.dart
+++ b/lib/src/timeline.dart
@@ -132,15 +132,16 @@ class Timeline {
   void _sessionKeyReceived(String sessionId) async {
     var decryptAtLeastOneEvent = false;
     final decryptFn = () async {
-      if (!room.client.encryptionEnabled) {
+      final encryption = room.client.encryption;
+      if (!room.client.encryptionEnabled || encryption == null) {
         return;
       }
       for (var i = 0; i < events.length; i++) {
         if (events[i].type == EventTypes.Encrypted &&
             events[i].messageType == MessageTypes.BadEncrypted &&
             events[i].content['session_id'] == sessionId) {
-          events[i] = await room.client.encryption
-              .decryptRoomEvent(room.id, events[i], store: true);
+          events[i] = await encryption.decryptRoomEvent(room.id, events[i],
+              store: true);
           if (events[i].type != EventTypes.Encrypted) {
             decryptAtLeastOneEvent = true;
           }
@@ -148,7 +149,7 @@ class Timeline {
       }
     };
     if (room.client.database != null) {
-      await room.client.database.transaction(decryptFn);
+      await room.client.database?.transaction(decryptFn);
     } else {
       await decryptFn();
     }
@@ -162,7 +163,7 @@ class Timeline {
           event.messageType == MessageTypes.BadEncrypted &&
           event.content['can_request_session'] == true) {
         try {
-          room.client.encryption.keyManager.maybeAutoRequest(room.id,
+          room.client.encryption?.keyManager.maybeAutoRequest(room.id,
               event.content['session_id'], event.content['sender_key']);
         } catch (_) {
           // dispose
diff --git a/lib/src/utils/commands_extension.dart b/lib/src/utils/commands_extension.dart
index 666c897e..7c4cc2ee 100644
--- a/lib/src/utils/commands_extension.dart
+++ b/lib/src/utils/commands_extension.dart
@@ -178,7 +178,7 @@ extension CommandsClientExtension on Client {
       return await args.room.client.setRoomStateWithKey(
         args.room.id,
         EventTypes.RoomMember,
-        args.room.client.userID,
+        args.room.client.userID!,
         currentEventJson,
       );
     });
@@ -191,7 +191,7 @@ extension CommandsClientExtension on Client {
       return await args.room.client.setRoomStateWithKey(
         args.room.id,
         EventTypes.RoomMember,
-        args.room.client.userID,
+        args.room.client.userID!,
         currentEventJson,
       );
     });
diff --git a/lib/src/utils/device_keys_list.dart b/lib/src/utils/device_keys_list.dart
index 7e3e217b..58f25985 100644
--- a/lib/src/utils/device_keys_list.dart
+++ b/lib/src/utils/device_keys_list.dart
@@ -68,17 +68,21 @@ class DeviceKeysList {
   }
 
   Future<KeyVerification> startVerification() async {
+    final encryption = client.encryption;
+    if (encryption == null) {
+      throw Exception('Encryption not enabled');
+    }
     if (userId != client.userID) {
       // in-room verification with someone else
       final roomId = await client.startDirectChat(userId);
-      if (roomId ==
-          null /* can be null as long as startDirectChat is not migrated */) {
+      if (roomId == null) {
         throw Exception('Unable to start new room');
       }
+
       final room =
           client.getRoomById(roomId) ?? Room(id: roomId, client: client);
-      final request = KeyVerification(
-          encryption: client.encryption, room: room, userId: userId);
+      final request =
+          KeyVerification(encryption: encryption, room: room, userId: userId);
       await request.start();
       // no need to add to the request client object. As we are doing a room
       // verification request that'll happen automatically once we know the transaction id
@@ -86,9 +90,9 @@ class DeviceKeysList {
     } else {
       // broadcast self-verification
       final request = KeyVerification(
-          encryption: client.encryption, userId: userId, deviceId: '*');
+          encryption: encryption, userId: userId, deviceId: '*');
       await request.start();
-      client.encryption.keyVerificationManager.addRequest(request);
+      encryption.keyVerificationManager.addRequest(request);
       return request;
     }
   }
@@ -314,13 +318,15 @@ abstract class SignableKey extends MatrixSignableKey {
 
   Future<void> setVerified(bool newVerified, [bool sign = true]) async {
     _verified = newVerified;
+    final encryption = client.encryption;
     if (newVerified &&
         sign &&
+        encryption != null &&
         client.encryptionEnabled &&
-        client.encryption.crossSigning.signable([this])) {
+        encryption.crossSigning.signable([this])) {
       // sign the key!
       // ignore: unawaited_futures
-      client.encryption.crossSigning.sign([this]);
+      encryption.crossSigning.sign([this]);
     }
   }
 
@@ -493,11 +499,16 @@ class DeviceKeys extends SignableKey {
     if (!isValid) {
       throw Exception('setVerification called on invalid key');
     }
+    final encryption = client.encryption;
+    if (encryption == null) {
+      throw Exception('setVerification called with disabled encryption');
+    }
+
     final request = KeyVerification(
-        encryption: client.encryption, userId: userId, deviceId: deviceId!);
+        encryption: encryption, userId: userId, deviceId: deviceId!);
 
     request.start();
-    client.encryption.keyVerificationManager.addRequest(request);
+    encryption.keyVerificationManager.addRequest(request);
     return request;
   }
 }
diff --git a/lib/src/utils/event_update.dart b/lib/src/utils/event_update.dart
index 11feef5c..922e90e2 100644
--- a/lib/src/utils/event_update.dart
+++ b/lib/src/utils/event_update.dart
@@ -49,12 +49,14 @@ class EventUpdate {
   });
 
   Future<EventUpdate> decrypt(Room room, {bool store = false}) async {
+    final encryption = room.client.encryption;
     if (content['type'] != EventTypes.Encrypted ||
-        !room.client.encryptionEnabled) {
+        !room.client.encryptionEnabled ||
+        encryption == null) {
       return this;
     }
     try {
-      final decrpytedEvent = await room.client.encryption.decryptRoomEvent(
+      final decrpytedEvent = await encryption.decryptRoomEvent(
           room.id, Event.fromJson(content, room),
           store: store, updateType: type);
       return EventUpdate(
diff --git a/lib/src/utils/uri_extension.dart b/lib/src/utils/uri_extension.dart
index e4d875a4..6202ad3b 100644
--- a/lib/src/utils/uri_extension.dart
+++ b/lib/src/utils/uri_extension.dart
@@ -24,7 +24,9 @@ extension MxcUriExtension on Uri {
   /// Returns a download Link to this content.
   Uri getDownloadLink(Client matrix) => isScheme('mxc')
       ? matrix.homeserver != null
-          ? matrix.homeserver.resolve('_matrix/media/r0/download/$host$path')
+          ? matrix.homeserver
+                  ?.resolve('_matrix/media/r0/download/$host$path') ??
+              Uri()
           : Uri()
       : this;
 
@@ -39,14 +41,15 @@ extension MxcUriExtension on Uri {
       ThumbnailMethod? method = ThumbnailMethod.crop,
       bool? animated = false}) {
     if (!isScheme('mxc')) return this;
-    if (matrix.homeserver == null) {
+    final homeserver = matrix.homeserver;
+    if (homeserver == null) {
       return Uri();
     }
     return Uri(
-      scheme: matrix.homeserver.scheme,
-      host: matrix.homeserver.host,
+      scheme: homeserver.scheme,
+      host: homeserver.host,
       path: '/_matrix/media/r0/thumbnail/$host$path',
-      port: matrix.homeserver.port,
+      port: homeserver.port,
       queryParameters: {
         if (width != null) 'width': width.round().toString(),
         if (height != null) 'height': height.round().toString(),
diff --git a/test/client_test.dart b/test/client_test.dart
index 2d5572d0..2e535cba 100644
--- a/test/client_test.dart
+++ b/test/client_test.dart
@@ -596,6 +596,7 @@ void main() {
       expect(client2.homeserver, client1.homeserver);
       expect(client2.deviceID, client1.deviceID);
       expect(client2.deviceName, client1.deviceName);
+      expect(client2.rooms.length, 2);
       if (client2.encryptionEnabled) {
         expect(client2.encryption.fingerprintKey,
             client1.encryption.fingerprintKey);
diff --git a/test/fake_database.dart b/test/fake_database.dart
index cd9f6714..a5dad91b 100644
--- a/test/fake_database.dart
+++ b/test/fake_database.dart
@@ -1,4 +1,3 @@
-// @dart=2.9
 /*
  *   Famedly Matrix SDK
  *   Copyright (C) 2019, 2020 Famedly GmbH
@@ -25,11 +24,11 @@ import 'package:matrix/src/database/hive_database.dart';
 import 'package:file/memory.dart';
 import 'package:hive/hive.dart';
 
-Future<DatabaseApi> getDatabase(Client _) => getHiveDatabase(_);
+Future<DatabaseApi> getDatabase(Client? _) => getHiveDatabase(_);
 
 bool hiveInitialized = false;
 
-Future<FamedlySdkHiveDatabase> getHiveDatabase(Client c) async {
+Future<FamedlySdkHiveDatabase> getHiveDatabase(Client? c) async {
   if (!hiveInitialized) {
     final fileSystem = MemoryFileSystem();
     final testHivePath =
@@ -38,7 +37,7 @@ Future<FamedlySdkHiveDatabase> getHiveDatabase(Client c) async {
     Hive.init(testHivePath);
     hiveInitialized = true;
   }
-  final db = FamedlySdkHiveDatabase('unit_test.${c.hashCode}');
+  final db = FamedlySdkHiveDatabase('unit_test.${c?.hashCode}');
   await db.open();
   return db;
 }