[FVS-88] unable to join a call (#506)

Author: kanat

packages/stream_video/lib/open_api/video/coordinator/model/user_response.dart

@@ -27,7 +27,7 @@ class UserResponse {
   /// Date/time of creation
   DateTime createdAt;
 
-  Map<String, Object> custom;
+  Map<String, Object?> custom;
 
   /// Date/time of deletion
   ///
@@ -137,7 +137,7 @@ class UserResponse {
 
       return UserResponse(
         createdAt: mapDateTime(json, r'created_at', '')!,
-        custom: mapCastOfType<String, Object>(json, r'custom')!,
+        custom: mapCastOfType<String, Object?>(json, r'custom')!,
         deletedAt: mapDateTime(json, r'deleted_at', ''),
         id: mapValueOfType<String>(json, r'id')!,
         image: mapValueOfType<String>(json, r'image'),

packages/stream_video/lib/src/models/call_metadata.dart

@@ -103,7 +103,7 @@ class CallMember with EquatableMixin {
 
   final String userId;
   final String role;
-  final Map<String, Object>? custom;
+  final Map<String, Object?> custom;
   final DateTime? createdAt;
   final DateTime? updatedAt;
   final DateTime? deletedAt;

packages/stream_video/lib/src/models/guest_created_data.dart

@@ -58,7 +58,7 @@ class UserResponseData with EquatableMixin {
   /// Date/time of creation
   final DateTime createdAt;
 
-  final Map<String, Object> custom;
+  final Map<String, Object?> custom;
 
   /// Date/time of deletion
   ///