fix annotation reply is null (#7103)

api/core/app/apps/advanced_chat/generate_task_pipeline.py

@@ -244,7 +244,11 @@ class AdvancedChatAppGenerateTaskPipeline(BasedGenerateTaskPipeline, WorkflowCyc
         :return:
         """
         for message in self._queue_manager.listen():
-            if message.event and hasattr(message.event, 'metadata') and message.event.metadata.get('is_answer_previous_node', False) and publisher:
+            if (message.event
+                    and hasattr(message.event, 'metadata')
+                    and message.event.metadata
+                    and message.event.metadata.get('is_answer_previous_node', False)
+                    and publisher):
                 publisher.publish(message=message)
             elif (hasattr(message.event, 'execution_metadata')
                   and message.event.execution_metadata