diff --git a/lib/src/voip_content.dart b/lib/src/voip_content.dart
index 887824c7..6f34969b 100644
--- a/lib/src/voip_content.dart
+++ b/lib/src/voip_content.dart
@@ -4,20 +4,19 @@ class CallReplacesTarget {
   String display_name;
   String avatar_url;
 
-  CallReplacesTarget();
-  factory CallReplacesTarget.fromJson(Map<String, dynamic> json) {
-    return CallReplacesTarget()
-      ..id = json['id'].toString()
-      ..display_name = json['display_name'].toString()
-      ..avatar_url = json['avatar_url'].toString();
-  }
-  Map<String, dynamic> toJson() {
-    return {
-      if (id != null) 'id': id,
-      if (display_name != null) 'display_name': display_name,
-      if (avatar_url != null) 'avatar_url': avatar_url,
-    };
-  }
+  CallReplacesTarget({this.id, this.display_name, this.avatar_url});
+  factory CallReplacesTarget.fromJson(Map<String, dynamic> json) =>
+      CallReplacesTarget(
+        id: json['id'].toString(),
+        display_name: json['display_name'].toString(),
+        avatar_url: json['avatar_url'].toString(),
+      );
+
+  Map<String, dynamic> toJson() => {
+        if (id != null) 'id': id,
+        if (display_name != null) 'display_name': display_name,
+        if (avatar_url != null) 'avatar_url': avatar_url,
+      };
 }
 
 /// MSC2747: VoIP call transfers
@@ -29,25 +28,28 @@ class CallReplaces {
   String await_call;
   String target_room;
 
-  CallReplaces();
-  factory CallReplaces.fromJson(Map<String, dynamic> json) {
-    return CallReplaces()
-      ..replacement_id = json['replacement_id'].toString()
-      ..create_call = json['create_call'].toString()
-      ..await_call = json['await_call'].toString()
-      ..target_room = json['target_room'].toString()
-      ..target_user = CallReplacesTarget.fromJson(json['target_user']);
-  }
+  CallReplaces({
+    this.replacement_id,
+    this.target_user,
+    this.create_call,
+    this.await_call,
+    this.target_room,
+  });
+  factory CallReplaces.fromJson(Map<String, dynamic> json) => CallReplaces(
+        replacement_id: json['replacement_id'].toString(),
+        create_call: json['create_call'].toString(),
+        await_call: json['await_call'].toString(),
+        target_room: json['target_room'].toString(),
+        target_user: CallReplacesTarget.fromJson(json['target_user']),
+      );
 
-  Map<String, dynamic> toJson() {
-    return {
-      if (replacement_id != null) 'replacement_id': replacement_id,
-      if (target_user != null) 'target_user': target_user.toJson(),
-      if (create_call != null) 'create_call': create_call,
-      if (await_call != null) 'await_call': await_call,
-      if (target_room != null) 'target_room': target_room,
-    };
-  }
+  Map<String, dynamic> toJson() => {
+        if (replacement_id != null) 'replacement_id': replacement_id,
+        if (target_user != null) 'target_user': target_user.toJson(),
+        if (create_call != null) 'create_call': create_call,
+        if (await_call != null) 'await_call': await_call,
+        if (target_room != null) 'target_room': target_room,
+      };
 }
 
 // TODO: Change to "sdp_stream_metadata" when MSC3077 is merged
@@ -58,18 +60,16 @@ const String sdpStreamMetadataKey = 'org.matrix.msc3077.sdp_stream_metadata';
 class CallCapabilities {
   bool transferee;
   bool dtmf;
-  CallCapabilities();
-  factory CallCapabilities.fromJson(Map<String, dynamic> json) {
-    return CallCapabilities()
-      ..dtmf = json['m.call.dtmf'] as bool ?? false
-      ..transferee = json['m.call.transferee'] as bool ?? false;
-  }
-  Map<String, dynamic> toJson() {
-    return {
-      if (transferee != null) 'm.call.transferee': transferee,
-      if (dtmf != null) 'm.call.dtmf': dtmf,
-    };
-  }
+  CallCapabilities({this.transferee, this.dtmf});
+  factory CallCapabilities.fromJson(Map<String, dynamic> json) =>
+      CallCapabilities(
+        dtmf: json['m.call.dtmf'] as bool ?? false,
+        transferee: json['m.call.transferee'] as bool ?? false,
+      );
+  Map<String, dynamic> toJson() => {
+        if (transferee != null) 'm.call.transferee': transferee,
+        if (dtmf != null) 'm.call.dtmf': dtmf,
+      };
 }
 
 /// MSC3077: Support for multi-stream VoIP
@@ -88,21 +88,19 @@ class SDPStreamPurpose {
   bool audio_muted;
   bool video_muted;
 
-  SDPStreamPurpose();
-  factory SDPStreamPurpose.fromJson(Map<String, dynamic> json) {
-    return SDPStreamPurpose()
-      ..audio_muted = json['audio_muted'] as bool ?? false
-      ..video_muted = json['video_muted'] as bool ?? false
-      ..purpose = json['purpose'] as String;
-  }
+  SDPStreamPurpose({this.purpose, this.audio_muted, this.video_muted});
+  factory SDPStreamPurpose.fromJson(Map<String, dynamic> json) =>
+      SDPStreamPurpose(
+        audio_muted: json['audio_muted'] as bool ?? false,
+        video_muted: json['video_muted'] as bool ?? false,
+        purpose: json['purpose'] as String,
+      );
 
-  Map<String, dynamic> toJson() {
-    return {
-      'purpose': purpose,
-      if (audio_muted != null) 'audio_muted': audio_muted,
-      if (video_muted != null) 'video_muted': video_muted,
-    };
-  }
+  Map<String, dynamic> toJson() => {
+        'purpose': purpose,
+        if (audio_muted != null) 'audio_muted': audio_muted,
+        if (video_muted != null) 'video_muted': video_muted,
+      };
 }
 
 class SDPStreamMetadataPurpose {
@@ -114,14 +112,11 @@ class SDPStreamMetadata {
   Map<String, SDPStreamPurpose> sdpStreamMetadatas;
   SDPStreamMetadata(this.sdpStreamMetadatas);
 
-  factory SDPStreamMetadata.fromJson(Map<String, dynamic> json) {
-    return SDPStreamMetadata(json
-        .map((key, value) => MapEntry(key, SDPStreamPurpose.fromJson(value))));
-  }
-  Map<String, dynamic> toJson() {
-    return sdpStreamMetadatas
-        .map((key, value) => MapEntry(key, value.toJson()));
-  }
+  factory SDPStreamMetadata.fromJson(Map<String, dynamic> json) =>
+      SDPStreamMetadata(json.map(
+          (key, value) => MapEntry(key, SDPStreamPurpose.fromJson(value))));
+  Map<String, dynamic> toJson() =>
+      sdpStreamMetadatas.map((key, value) => MapEntry(key, value.toJson()));
 }
 
 /// MSC3086: Asserted identity on VoIP calls
@@ -130,19 +125,16 @@ class AssertedIdentity {
   String id;
   String displayName;
   String avatarUrl;
-  AssertedIdentity();
-  factory AssertedIdentity.fromJson(Map<String, dynamic> json) {
-    return AssertedIdentity()
-      ..displayName = json['display_name'] as String
-      ..id = json['id'] as String
-      ..avatarUrl = json['avatar_url'] as String;
-  }
-  Map<String, dynamic> toJson() {
-    return {
-      if (displayName != null) 'display_name': displayName,
-      if (id != null) 'id': id,
-      if (avatarUrl != null) 'avatar_url': avatarUrl,
-    };
-  }
+  AssertedIdentity({this.id, this.displayName, this.avatarUrl});
+  factory AssertedIdentity.fromJson(Map<String, dynamic> json) =>
+      AssertedIdentity(
+        displayName: json['display_name'] as String,
+        id: json['id'] as String,
+        avatarUrl: json['avatar_url'] as String,
+      );
+  Map<String, dynamic> toJson() => {
+        if (displayName != null) 'display_name': displayName,
+        if (id != null) 'id': id,
+        if (avatarUrl != null) 'avatar_url': avatarUrl,
+      };
 }
-