Update passthrough.py (#15252)

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libs/core/langchain_core/runnables/passthrough.py

@@ -647,7 +647,7 @@ def transform(
         self,
         input: Iterator[Dict[str, Any]],
         config: Optional[RunnableConfig] = None,
-        **kwargs: Any | None,
+        **kwargs: Any,
     ) -> Iterator[Dict[str, Any]]:
         yield from self._transform_stream_with_config(
             input, self._transform, config, **kwargs