diff --git a/python/packages/core/agent_framework/_tools.py b/python/packages/core/agent_framework/_tools.py
index 93722a8987..1605c5443d 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_none=False
                         )
                 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_none=False)
                 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_none=False)
         else:
             args = dict(parsed_args)
         args = _validate_arguments_against_schema(
diff --git a/python/packages/core/agent_framework/_types.py b/python/packages/core/agent_framework/_types.py
index ce47f5fc8e..048551752b 100644
--- a/python/packages/core/agent_framework/_types.py
+++ b/python/packages/core/agent_framework/_types.py
@@ -1973,11 +1973,35 @@ def _coalesce_text_content(contents: list[Content], type_str: Literal["text", "t
     contents.extend(coalesced_contents)
 
 
+def _coalesce_code_interpreter_content(contents: list[Content]) -> None:
+    """Coalesce code_interpreter_tool_call items with the same call_id into a single item."""
+    if not contents:
+        return
+    seen: dict[str, Content] = {}
+    coalesced: list[Content] = []
+    for content in contents:
+        if content.type == "code_interpreter_tool_call" and content.call_id:
+            if content.call_id in seen:
+                existing = seen[content.call_id]
+                if content.inputs:
+                    if existing.inputs is None:
+                        existing.inputs = []
+                    existing.inputs.extend(content.inputs)
+            else:
+                seen[content.call_id] = content
+                coalesced.append(content)
+        else:
+            coalesced.append(content)
+    contents.clear()
+    contents.extend(coalesced)
+
+
 def _finalize_response(response: ChatResponse | AgentResponse) -> None:
     """Finalizes the response by performing any necessary post-processing."""
     for msg in response.messages:
         _coalesce_text_content(msg.contents, "text")
         _coalesce_text_content(msg.contents, "text_reasoning")
+        _coalesce_code_interpreter_content(msg.contents)
 
 
 # region ContinuationToken
diff --git a/python/packages/core/tests/core/test_tools.py b/python/packages/core/tests/core/test_tools.py
index b3762bf4ef..df161a056d 100644
--- a/python/packages/core/tests/core/test_tools.py
+++ b/python/packages/core/tests/core/test_tools.py
@@ -1,4 +1,5 @@
 # Copyright (c) Microsoft. All rights reserved.
+import asyncio
 from typing import Annotated, Any, Literal, get_args, get_origin
 from unittest.mock import Mock
 
@@ -1462,4 +1463,20 @@ def test_skip_parsing_is_singleton() -> None:
     assert repr(SKIP_PARSING) == "SKIP_PARSING"
 
 
+def test_invoke_preserves_explicit_none_arguments() -> None:
+    """Optional parameters explicitly set to None must not be stripped before invocation."""
+
+    @tool
+    def greet(name: str, greeting: str | None = None) -> str:
+        return f"{greeting or 'Hello'}, {name}!"
+
+    result = asyncio.run(greet.invoke(arguments={"name": "World", "greeting": None}))
+    assert isinstance(result, list)
+    assert result[0].text == "Hello, World!"
+
+    result = asyncio.run(greet.invoke(arguments={"name": "World"}))
+    assert isinstance(result, list)
+    assert result[0].text == "Hello, World!"
+
+
 # endregion