fix: 3pid api bugs

lib/matrix_api/matrix_api.dart

@@ -517,15 +517,15 @@ class MatrixApi {
   /// https://matrix.org/docs/spec/client_server/r0.6.0#post-matrix-client-r0-account-3pid-delete
   Future<IdServerUnbindResult> deleteThirdPartyIdentifier(
     String address,
-    ThirdPartyIdentifierMedium medium,
+    ThirdPartyIdentifierMedium medium, {
     String idServer,
-  ) async {
+  }) async {
     final response = await request(
         RequestType.POST, '/client/r0/account/3pid/delete',
         data: {
           'address': address,
           'medium': describeEnum(medium),
-          'id_server': idServer,
+          if (idServer != null) 'id_server': idServer,
         });
     return IdServerUnbindResult.values.firstWhere(
       (i) => describeEnum(i) == response['id_server_unbind_result'],

lib/matrix_api/model/third_party_identifier.dart

@@ -16,14 +16,17 @@
  *   along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+import 'package:famedlysdk/matrix_api.dart';
+
 class ThirdPartyIdentifier {
-  String medium;
+  ThirdPartyIdentifierMedium medium;
   String address;
   int validatedAt;
   int addedAt;
 
   ThirdPartyIdentifier.fromJson(Map<String, dynamic> json) {
-    medium = json['medium'];
+    medium = ThirdPartyIdentifierMedium.values
+        .firstWhere((medium) => describeEnum(medium) == json['medium']);
     address = json['address'];
     validatedAt = json['validated_at'];
     addedAt = json['added_at'];
@@ -31,7 +34,7 @@ class ThirdPartyIdentifier {
 
   Map<String, dynamic> toJson() {
     final data = <String, dynamic>{};
-    data['medium'] = medium;
+    data['medium'] = describeEnum(medium);
     data['address'] = address;
     data['validated_at'] = validatedAt;
     data['added_at'] = addedAt;

test/matrix_api_test.dart

@@ -287,7 +287,7 @@ void main() {
       final response = await matrixApi.deleteThirdPartyIdentifier(
         'alice@example.com',
         ThirdPartyIdentifierMedium.email,
-        'https://example.com',
+        idServer: 'https://example.com',
       );
       expect(response, IdServerUnbindResult.success);
       matrixApi.homeserver = matrixApi.accessToken = null;