fix: handle Python 3.10+ union syntax (T | None) in Optional unwrap

Author: yuvrajangadsingh

src/google/adk/tools/function_tool.py

@@ -16,13 +16,21 @@
 
 import inspect
 import logging
+import sys
 from typing import Any
 from typing import Callable
 from typing import get_args
 from typing import get_origin
 from typing import Optional
 from typing import Union
 
+if sys.version_info >= (3, 10):
+  from types import UnionType
+
+  _UNION_TYPES = (Union, UnionType)
+else:
+  _UNION_TYPES = (Union,)
+
 from google.genai import types
 import pydantic
 from typing_extensions import override
@@ -127,8 +135,8 @@ def _preprocess_args(
       target_type = param.annotation
       is_optional = False
 
-      # Handle Optional[T] (Union[T, None]) - unwrap to get inner type
-      if get_origin(param.annotation) is Union:
+      # Handle Optional[T] (Union[T, None]) and T | None (Python 3.10+)
+      if get_origin(param.annotation) in _UNION_TYPES:
         union_args = get_args(param.annotation)
         non_none_types = [arg for arg in union_args if arg is not type(None)]
         if len(non_none_types) == 1: