fix(edit_topic): handle null exception in state

- Updated EditTopicState to handle null exception.
- Prevents potential crashes from null values.

Author: fulleni

lib/content_management/bloc/edit_topic/edit_topic_state.dart

@@ -62,7 +62,7 @@ final class EditTopicState extends Equatable {
       description: description ?? this.description,
       iconUrl: iconUrl ?? this.iconUrl,
       contentStatus: contentStatus ?? this.contentStatus,
-      exception: exception,
+      exception: exception ?? this.exception,
       updatedTopic: updatedTopic ?? this.updatedTopic,
     );
   }