diff --git a/metagpt/actions/action_node.py b/metagpt/actions/action_node.py
index 4f61af4ed..ca41c76a5 100644
--- a/metagpt/actions/action_node.py
+++ b/metagpt/actions/action_node.py
@@ -469,8 +469,10 @@ class ActionNode:
             return dict()
 
         prompt = template.format(
-            nodes_output=json.dumps(nodes_output, ensure_ascii=False), tag=TAG, constraint=FORMAT_CONSTRAINT,
-            prompt_schema="json"
+            nodes_output=json.dumps(nodes_output, ensure_ascii=False),
+            tag=TAG,
+            constraint=FORMAT_CONSTRAINT,
+            prompt_schema="json",
         )
 
         content = await self.llm.aask(prompt)
@@ -568,7 +570,7 @@ class ActionNode:
             example=example,
             instruction=instruction,
             constraint=FORMAT_CONSTRAINT,
-            prompt_schema="json"
+            prompt_schema="json",
         )
 
         # step2, use `_aask_v1` to get revise structure result
diff --git a/metagpt/schema.py b/metagpt/schema.py
index 0a7a07b03..22bb359b6 100644
--- a/metagpt/schema.py
+++ b/metagpt/schema.py
@@ -232,7 +232,7 @@ class Message(BaseModel):
         return any_to_str_set(send_to if send_to else {MESSAGE_ROUTE_TO_ALL})
 
     @field_serializer("instruct_content", mode="plain")
-    def ser_instruct_content(self, ic: BaseModel) -> Union[str, None]:
+    def ser_instruct_content(self, ic: BaseModel) -> Union[dict, None]:
         ic_dict = None
         if ic:
             # compatible with custom-defined ActionOutput
diff --git a/tests/metagpt/serialize_deserialize/test_write_prd.py b/tests/metagpt/serialize_deserialize/test_write_prd.py
index 820ee237c..afc483e9a 100644
--- a/tests/metagpt/serialize_deserialize/test_write_prd.py
+++ b/tests/metagpt/serialize_deserialize/test_write_prd.py
@@ -18,5 +18,5 @@ async def test_action_serdeser(new_filename):
 
     new_action = WritePRD(**ser_action_dict)
     assert new_action.name == "WritePRD"
-    action_output = await new_action.run(with_messages=Message(content="write a cli snake game"))
-    assert len(action_output.content) > 0
+    with pytest.raises(FileNotFoundError):
+        await new_action.run(with_messages=Message(content="write a cli snake game"))