From 58e40673d5548908f73d8ff6313d45012d694ff6 Mon Sep 17 00:00:00 2001
From: Yufeng He <40085740+he-yufeng@users.noreply.github.com>
Date: Mon, 1 Jun 2026 06:48:56 +0800
Subject: [PATCH] fix(python): preserve null tool arguments

---
 .../packages/core/agent_framework/_tools.py   |  6 ++--
 python/packages/core/tests/core/test_tools.py | 31 +++++++++++++++++++
 2 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/python/packages/core/agent_framework/_tools.py b/python/packages/core/agent_framework/_tools.py
index 93722a8987..f702ed0d2c 100644
--- a/python/packages/core/agent_framework/_tools.py
+++ b/python/packages/core/agent_framework/_tools.py
@@ -636,7 +636,7 @@ async def invoke(
                     parsed_arguments = dict(arguments)
                     if self.input_model is not None and not self._schema_supplied:
                         parsed_arguments = self.input_model.model_validate(parsed_arguments).model_dump(
-                            exclude_none=True
+                            exclude_unset=True
                         )
                 elif isinstance(arguments, BaseModel):
                     if (
@@ -645,7 +645,7 @@ async def invoke(
                         and not isinstance(arguments, self.input_model)
                     ):
                         raise TypeError(f"Expected {self.input_model.__name__}, got {type(arguments).__name__}")
-                    parsed_arguments = arguments.model_dump(exclude_none=True)
+                    parsed_arguments = arguments.model_dump(exclude_unset=True)
                 else:
                     raise TypeError(
                         f"Expected mapping-like arguments for tool '{self.name}', got {type(arguments).__name__}"
@@ -1492,7 +1492,7 @@ async def _auto_invoke_function(
         runtime_kwargs["session"] = invocation_session
     try:
         if not cast(bool, getattr(tool, "_schema_supplied", False)) and tool.input_model is not None:
-            args = tool.input_model.model_validate(parsed_args).model_dump(exclude_none=True)
+            args = tool.input_model.model_validate(parsed_args).model_dump(exclude_unset=True)
         else:
             args = dict(parsed_args)
         args = _validate_arguments_against_schema(
diff --git a/python/packages/core/tests/core/test_tools.py b/python/packages/core/tests/core/test_tools.py
index b3762bf4ef..cf5e36d82f 100644
--- a/python/packages/core/tests/core/test_tools.py
+++ b/python/packages/core/tests/core/test_tools.py
@@ -15,6 +15,7 @@
 )
 from agent_framework._middleware import FunctionInvocationContext
 from agent_framework._tools import (
+    _auto_invoke_function,
     _parse_annotation,
     _parse_inputs,
     _tools_to_dict,
@@ -183,6 +184,36 @@ def search(query: str, max_results: int = 10) -> str:
         await search.invoke(arguments={"query": "hello", "max_results": "three"})
 
 
+async def test_tool_invoke_preserves_required_null_argument():
+    @tool
+    def get_weather(location: str, unit: Literal["C", "F"] | None) -> str:
+        return f"{location}:{unit}"
+
+    result = await get_weather.invoke(arguments={"location": "Seattle", "unit": None})
+
+    assert result[0].text == "Seattle:None"
+
+
+async def test_auto_function_call_preserves_required_null_argument():
+    @tool
+    def get_weather(location: str, unit: Literal["C", "F"] | None) -> str:
+        return f"{location}:{unit}"
+
+    result = await _auto_invoke_function(
+        Content.from_function_call(
+            call_id="call_1",
+            name="get_weather",
+            arguments='{"location": "Seattle", "unit": null}',
+        ),
+        config={},
+        tool_map={"get_weather": get_weather},
+    )
+
+    assert result.type == "function_result"
+    assert result.result == "Seattle:None"
+    assert result.exception is None
+
+
 def test_tool_decorator_with_json_schema_preserves_custom_properties():
     """Test schema passthrough keeps custom JSON schema properties."""