diff --git a/api/core/app/entities/task_entities.py b/api/core/app/entities/task_entities.py
index 5de8793cfb..64af4bf8c6 100644
--- a/api/core/app/entities/task_entities.py
+++ b/api/core/app/entities/task_entities.py
@@ -122,7 +122,7 @@ class MessageEndStreamResponse(StreamResponse):
     """
     event: StreamEvent = StreamEvent.MESSAGE_END
     id: str
-    metadata: Optional[dict] = None
+    metadata: dict = {}
 
 
 class MessageFileStreamResponse(StreamResponse):