diff --git a/agentlego/tools/remote.py b/agentlego/tools/remote.py
index 89ad8521..99789b4b 100644
--- a/agentlego/tools/remote.py
+++ b/agentlego/tools/remote.py
@@ -145,6 +145,12 @@ def apply(self, *args, **kwargs):
                 content = response.content.decode()
             raise RuntimeError(f'Failed to call the remote tool `{self.name}` '
                                f'because of {response.reason}.\nResponse: {content}')
+
+        response_schema = self.operation.responses
+        if response_schema is None or response_schema.get('200') is None:
+            # Directly use string if the response schema is not specified
+            return response.text
+
         try:
             response = response.json()
         except requests.JSONDecodeError as e:
@@ -152,11 +158,6 @@ def apply(self, *args, **kwargs):
                                'because of unknown response.\n'
                                f'Response: {response.content.decode()}') from e
 
-        response_schema = self.operation.responses
-        if response_schema is None or response_schema.get('200') is None:
-            # Directly use string if the response schema is not specified
-            return str(response)
-
         out_props = response_schema['200'].properties
 
         if isinstance(out_props, APIResponseProperty):
diff --git a/agentlego/utils/openapi/api_model.py b/agentlego/utils/openapi/api_model.py
index 2b7a2a82..1e14300f 100644
--- a/agentlego/utils/openapi/api_model.py
+++ b/agentlego/utils/openapi/api_model.py
@@ -498,8 +498,11 @@ def _process_supported_media_type(
         return properties
 
     @classmethod
-    def from_response(cls, response: Response, spec: OpenAPISpec) -> 'APIResponse':
+    def from_response(cls, response: Response,
+                      spec: OpenAPISpec) -> Optional['APIResponse']:
         """Instantiate from an OpenAPI Response."""
+        if response.content is None:
+            return None
         # Only handle one potential response payload style.
         media_type = next(
             (k for k in response.content if k in _SUPPORTED_RESPONSE_MEDIA_TYPES), None)
@@ -545,7 +548,7 @@ class APIOperation(BaseModel):
     request_body: Optional[APIRequestBody] = Field(alias='request_body')
     """The request body of the operation."""
 
-    responses: Optional[Dict[str, APIResponse]] = Field(alias='responses')
+    responses: Optional[Dict[str, Optional[APIResponse]]] = Field(alias='responses')
 
     @staticmethod
     def _get_properties_from_parameters(parameters: List[Parameter],