fix(ui): fix tests

packages/stream_chat_flutter/lib/src/message_list_view.dart

@@ -969,7 +969,7 @@ class _MessageListViewState extends State<MessageListView> {
     }
 
     final userId = StreamChat.of(context).currentUser!.id;
-    final isMyMessage = message.user!.id == userId;
+    final isMyMessage = message.user?.id == userId;
     final nextMessage = index - 1 >= 0 ? messages[index - 1] : null;
     final isNextUserSame =
         nextMessage != null && message.user!.id == nextMessage.user!.id;

packages/stream_chat_flutter/lib/src/message_widget.dart

@@ -987,7 +987,7 @@ class _MessageWidgetState extends State<MessageWidget>
       return widget.usernameBuilder!(context, widget.message);
     }
     return Text(
-      widget.message.user!.name,
+      widget.message.user?.name ?? '',
       maxLines: 1,
       key: usernameKey,
       style: widget.messageTheme.messageAuthorStyle,