task: added warning when none is called in intervention handler

python/packages/autogen-core/src/autogen_core/base/intervention.py

@@ -1,5 +1,5 @@
+import warnings
 from typing import Any, Awaitable, Callable, Protocol, final
-
 from autogen_core.base import AgentId
 
 __all__ = [
@@ -14,6 +14,27 @@
 class DropMessage: ...
 
 
+def warn_if_none(result: Any, handler_name: str) -> Any:
+    """
+    Utility function to check if the intervention handler returned None and issue a warning.
+
+    Args:
+        result: The return value from the intervention handler
+        handler_name: Name of the intervention handler method for the warning message
+
+    Returns:
+        The original result value
+    """
+    if result is None:
+        warnings.warn(
+            f"Intervention handler {handler_name} returned None. This might be unintentional. "
+            "Consider returning the original message or DropMessage explicitly.",
+            RuntimeWarning,
+            stacklevel=2
+        )
+    return result
+
+
 InterventionFunction = Callable[[Any], Any | Awaitable[type[DropMessage]]]
 
 
@@ -27,10 +48,13 @@ async def on_response(
 
 class DefaultInterventionHandler(InterventionHandler):
     async def on_send(self, message: Any, *, sender: AgentId | None, recipient: AgentId) -> Any | type[DropMessage]:
-        return message
+        result = message
+        return warn_if_none(result, "on_send")
 
     async def on_publish(self, message: Any, *, sender: AgentId | None) -> Any | type[DropMessage]:
-        return message
+        result = message
+        return warn_if_none(result, "on_publish")
 
     async def on_response(self, message: Any, *, sender: AgentId, recipient: AgentId | None) -> Any | type[DropMessage]:
-        return message
+        result = message
+        return warn_if_none(result, "on_response")