refactor: apply Gemini review round 2 feedback

Author: yuvrajangadsingh

src/google/adk/tools/function_tool.py

@@ -142,7 +142,7 @@ def _preprocess_args(
       if inspect.isclass(target_type) and issubclass(
           target_type, pydantic.BaseModel
       ):
-        if args[param_name] is None:
+        if args[param_name] is None and is_optional:
           continue
         if not isinstance(args[param_name], target_type):
           try:
@@ -173,10 +173,16 @@ def _preprocess_args(
             f"Parameter '{param_name}': expected type '{target_type}',"
             f' validation error: {e}'
         )
-      except (TypeError, NameError):
+      except (TypeError, NameError) as e:
         # TypeAdapter could not handle this annotation (e.g. a forward
-        # reference string). Skip validation silently.
-        pass
+        # reference string). Skip validation but log a warning.
+        logger.warning(
+            "Skipping validation for parameter '%s' due to unhandled"
+            " annotation type '%s': %s",
+            param_name,
+            target_type,
+            e,
+        )
 
     return converted_args, validation_errors
 

tests/unittests/tools/test_function_tool_arg_validation.py

@@ -155,10 +155,12 @@ def test_multiple_param_errors(self):
     args, errors = tool._preprocess_args(
         {"name": 123, "count": "not_a_number", "flag": "not_a_bool"}
     )
-    # name: int->str coercion might fail in strict, but lax mode might
-    # handle it. count: "not_a_number"->int will fail. flag: depends on
-    # pydantic behavior.
+    # All three fail: pydantic rejects int->str, "not_a_number"->int,
+    # and "not_a_bool"->bool.
+    assert len(errors) == 3
+    assert any("name" in e for e in errors)
     assert any("count" in e for e in errors)
+    assert any("flag" in e for e in errors)
 
 
 # --- run_async integration tests ---