Python: Fix response_format crash on background polling with empty text

python/packages/core/agent_framework/_types.py

@@ -1957,6 +1957,8 @@ class ContinuationToken(TypedDict):
 def _parse_structured_response_value(text: str, response_format: Any | None) -> Any | None:
     if response_format is None:
         return None
+    if not text:
+        return None
     if isinstance(response_format, type) and issubclass(response_format, BaseModel):
         return response_format.model_validate_json(text)
     if isinstance(response_format, Mapping):

python/packages/core/tests/core/test_types.py

@@ -39,6 +39,7 @@
     _get_data_bytes,
     _get_data_bytes_as_str,
     _parse_content_list,
+    _parse_structured_response_value,
     _validate_uri,
     add_usage_details,
     validate_tool_mode,
@@ -813,6 +814,32 @@ def test_chat_response_with_mapping_response_format() -> None:
     assert response.value["response"] == "Hello"
 
 
+def test_parse_structured_response_value_empty_text_with_pydantic_model() -> None:
+    """Empty text should return None instead of raising when response_format is a Pydantic model."""
+    result = _parse_structured_response_value("", OutputModel)
+    assert result is None
+
+
+def test_parse_structured_response_value_empty_text_with_mapping() -> None:
+    """Empty text should return None instead of raising when response_format is a mapping."""
+    result = _parse_structured_response_value("", {"type": "object"})
+    assert result is None
+
+
+def test_chat_response_value_with_empty_text_and_response_format() -> None:
+    """ChatResponse.value should return None when text is empty and response_format is set."""
+    message = Message(role="assistant", contents=[""])
+    response = ChatResponse(messages=message, response_format=OutputModel)
+    assert response.value is None
+
+
+def test_agent_response_value_with_empty_text_and_response_format() -> None:
+    """AgentResponse.value should return None when text is empty and response_format is set."""
+    message = Message(role="assistant", contents=[""])
+    response = AgentResponse(messages=message, response_format=OutputModel)
+    assert response.value is None
+
+
 def test_chat_response_value_raises_on_invalid_schema():
     """Test that value property raises ValidationError with field constraint details."""