fix: In State schema validation use != instead of is not for checking the type of messages (#9454)

* Use != instead of is not

* Add reno

* Use more == instead of is

* Fix mypy

haystack/components/agents/state/state.py

@@ -69,7 +69,7 @@ def _validate_schema(schema: Dict[str, Any]) -> None:
             raise ValueError(f"StateSchema: 'type' for key '{param}' must be a Python type, got {definition['type']}")
         if definition.get("handler") is not None and not callable(definition["handler"]):
             raise ValueError(f"StateSchema: 'handler' for key '{param}' must be callable or None")
-        if param == "messages" and definition["type"] is not List[ChatMessage]:
+        if param == "messages" and definition["type"] != List[ChatMessage]:
             raise ValueError(f"StateSchema: 'messages' must be of type List[ChatMessage], got {definition['type']}")
 
 

haystack/components/agents/state/state_utils.py

@@ -31,7 +31,7 @@ def _is_valid_type(obj: Any) -> bool:
         False
     """
     # Handle Union types (including Optional)
-    if hasattr(obj, "__origin__") and obj.__origin__ is Union:
+    if hasattr(obj, "__origin__") and obj.__origin__ == Union:
         return True
 
     # Handle normal classes and generic types
@@ -45,7 +45,7 @@ def _is_list_type(type_hint: Any) -> bool:
     :param type_hint: The type hint to check
     :return: True if the type hint represents a list, False otherwise
     """
-    return type_hint is list or (hasattr(type_hint, "__origin__") and get_origin(type_hint) is list)
+    return type_hint == list or (hasattr(type_hint, "__origin__") and get_origin(type_hint) == list)
 
 
 def merge_lists(current: Union[List[T], T, None], new: Union[List[T], T]) -> List[T]:

haystack/components/generators/chat/hugging_face_local.py

@@ -422,7 +422,7 @@ class HuggingFaceLocalChatGenerator:
         replies = [o.get("generated_text", "") for o in output]
 
         # Remove stop words from replies if present
-        for stop_word in stop_words:
+        for stop_word in stop_words or []:
             replies = [reply.replace(stop_word, "").rstrip() for reply in replies]
 
         chat_messages = [

releasenotes/notes/fix-state-validate-schema-5ae41ce9c82de61a.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Fix type comparison in schema validation by replacing `is not` with `!=` when checking the type `List[ChatMessage]`.
+    This prevents false mismatches due to Python's `is` operator comparing object identity instead of equality.