diff --git a/packages/stream_chat_flutter_core/lib/src/channel_list_core.dart b/packages/stream_chat_flutter_core/lib/src/channel_list_core.dart
index 393c3686..b77ef394 100644
--- a/packages/stream_chat_flutter_core/lib/src/channel_list_core.dart
+++ b/packages/stream_chat_flutter_core/lib/src/channel_list_core.dart
@@ -66,7 +66,11 @@ class ChannelListCore extends StatefulWidget {
     this.sort,
     this.pagination,
     this.channelListController,
-  }) : super(key: key);
+  })  : assert(errorBuilder != null),
+        assert(emptyBuilder != null),
+        assert(loadingBuilder != null),
+        assert(listBuilder != null),
+        super(key: key);
 
   /// A [ChannelListController] allows reloading and pagination.
   /// Use [ChannelListController.loadData] and [ChannelListController.paginateData] respectively for reloading and pagination.
diff --git a/packages/stream_chat_flutter_core/lib/src/channels_bloc.dart b/packages/stream_chat_flutter_core/lib/src/channels_bloc.dart
index 987e06f9..7009234b 100644
--- a/packages/stream_chat_flutter_core/lib/src/channels_bloc.dart
+++ b/packages/stream_chat_flutter_core/lib/src/channels_bloc.dart
@@ -23,7 +23,8 @@ class ChannelsBloc extends StatefulWidget {
     this.lockChannelsOrder = false,
     this.channelsComparator,
     this.shouldAddChannel,
-  }) : super(key: key);
+  })  : assert(child != null),
+        super(key: key);
 
   /// The widget child
   final Widget child;
diff --git a/packages/stream_chat_flutter_core/lib/src/message_list_core.dart b/packages/stream_chat_flutter_core/lib/src/message_list_core.dart
index 5856575c..64e8f255 100644
--- a/packages/stream_chat_flutter_core/lib/src/message_list_core.dart
+++ b/packages/stream_chat_flutter_core/lib/src/message_list_core.dart
@@ -54,17 +54,21 @@ import 'stream_channel.dart';
 /// The widget uses a [ListView.custom] to render the list of channels.
 ///
 class MessageListCore extends StatefulWidget {
-  /// Instantiate a new [MessageListView]
+  /// Instantiate a new [MessageListView].
   MessageListCore({
     Key key,
-    this.showScrollToBottom = true,
-    this.parentMessage,
     @required this.loadingBuilder,
     @required this.emptyBuilder,
     @required this.messageListBuilder,
     @required this.errorWidgetBuilder,
+    this.showScrollToBottom = true,
+    this.parentMessage,
     this.messageListController,
-  }) : super(key: key);
+  })  : assert(loadingBuilder != null),
+        assert(emptyBuilder != null),
+        assert(messageListBuilder != null),
+        assert(errorWidgetBuilder != null),
+        super(key: key);
 
   /// A [MessageListController] allows pagination.
   /// Use [ChannelListController.paginateData] pagination.
diff --git a/packages/stream_chat_flutter_core/lib/src/message_search_bloc.dart b/packages/stream_chat_flutter_core/lib/src/message_search_bloc.dart
index a6a73012..6458bebf 100644
--- a/packages/stream_chat_flutter_core/lib/src/message_search_bloc.dart
+++ b/packages/stream_chat_flutter_core/lib/src/message_search_bloc.dart
@@ -16,7 +16,8 @@ class MessageSearchBloc extends StatefulWidget {
   const MessageSearchBloc({
     Key key,
     @required this.child,
-  }) : super(key: key);
+  })  : assert(child != null),
+        super(key: key);
 
   /// The widget child
   final Widget child;
diff --git a/packages/stream_chat_flutter_core/lib/src/message_search_list_core.dart b/packages/stream_chat_flutter_core/lib/src/message_search_list_core.dart
index 26ee58c1..e3d98426 100644
--- a/packages/stream_chat_flutter_core/lib/src/message_search_list_core.dart
+++ b/packages/stream_chat_flutter_core/lib/src/message_search_list_core.dart
@@ -50,7 +50,11 @@ class MessageSearchListCore extends StatefulWidget {
     this.paginationParams,
     this.messageFilters,
     this.messageSearchListController,
-  }) : super(key: key);
+  })  : assert(emptyBuilder != null),
+        assert(errorBuilder != null),
+        assert(loadingBuilder != null),
+        assert(childBuilder != null),
+        super(key: key);
 
   /// A [MessageSearchListController] allows reloading and pagination.
   /// Use [MessageSearchListController.loadData] and [MessageSearchListController.paginateData] respectively for reloading and pagination.
diff --git a/packages/stream_chat_flutter_core/lib/src/stream_chat_core.dart b/packages/stream_chat_flutter_core/lib/src/stream_chat_core.dart
index d454d8c9..fbdc6d86 100644
--- a/packages/stream_chat_flutter_core/lib/src/stream_chat_core.dart
+++ b/packages/stream_chat_flutter_core/lib/src/stream_chat_core.dart
@@ -40,7 +40,9 @@ class StreamChatCore extends StatefulWidget {
     Key key,
     @required this.client,
     @required this.child,
-  }) : super(key: key);
+  })  : assert(client != null),
+        assert(child != null),
+        super(key: key);
 
   /// Instance of Stream Chat Client containing information about the current
   /// application.
diff --git a/packages/stream_chat_flutter_core/lib/src/user_list_core.dart b/packages/stream_chat_flutter_core/lib/src/user_list_core.dart
index a9398d89..23140258 100644
--- a/packages/stream_chat_flutter_core/lib/src/user_list_core.dart
+++ b/packages/stream_chat_flutter_core/lib/src/user_list_core.dart
@@ -50,7 +50,6 @@ import 'package:stream_chat_flutter_core/src/users_bloc.dart';
 /// [UsersBloc] must be the ancestor of this widget. This is necessary since
 /// [UserListCore] depends on functionality contained within [UsersBloc].
 ///
-/// The widget uses a [ListView.separated], [GridView.builder] to render the list, grid of channels.
 /// The parameters [listBuilder], [loadingBuilder], [emptyBuilder] and [errorBuilder] must all be supplied
 /// and not null.
 class UserListCore extends StatefulWidget {
@@ -67,7 +66,11 @@ class UserListCore extends StatefulWidget {
     this.pagination,
     this.groupAlphabetically = false,
     this.userListController,
-  }) : super(key: key);
+  })  : assert(errorBuilder != null),
+        assert(emptyBuilder != null),
+        assert(loadingBuilder != null),
+        assert(listBuilder != null),
+        super(key: key);
 
   /// A [UserListController] allows reloading and pagination.
   /// Use [UserListController.loadData] and [UserListController.paginateData] respectively for reloading and pagination.
diff --git a/packages/stream_chat_flutter_core/lib/src/users_bloc.dart b/packages/stream_chat_flutter_core/lib/src/users_bloc.dart
index 359985b3..19c4a026 100644
--- a/packages/stream_chat_flutter_core/lib/src/users_bloc.dart
+++ b/packages/stream_chat_flutter_core/lib/src/users_bloc.dart
@@ -16,7 +16,8 @@ class UsersBloc extends StatefulWidget {
   const UsersBloc({
     Key key,
     @required this.child,
-  }) : super(key: key);
+  })  : assert(child != null),
+        super(key: key);
 
   /// The widget child
   final Widget child;