Python: Fix auto function calling stripping explicit null arguments (fixes #5934)

[hanhan761]

Summary

Changes exclude_none=True to exclude_none=False in FunctionTool.invoke() and _auto_invoke_function() to preserve explicitly-provided
ull values. When a model passes {"param": null} for a required-but-nullable parameter, exclude_none=True strips the key, causing the schema validation to report it as "missing required argument".

Root Cause

model_dump(exclude_none=True) cannot distinguish between "field was never provided" (default None) and "field was explicitly set to None". This splits the model's intent when it provides
ull for optional parameters.

Changes

• python/packages/core/agent_framework/_tools.py: Changed exclude_none=True to exclude_none=False in 3 locations (lines 639, 648, 1495)
• python/packages/core/tests/core/test_tools.py: Added est_invoke_preserves_explicit_none_arguments test

Issue

Fixes #5934

Verification

• New test est_invoke_preserves_explicit_none_arguments passes
• All existing tests in test_tools.py continue to pass

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Fixes an issue where explicit None values for optional tool arguments were being stripped before invocation, causing them to be treated as missing.

Changes:

• Changed exclude_none=True to exclude_none=False in three model_dump calls within _tools.py so explicit None values are preserved.
• Added a test verifying that None-valued optional parameters are passed through to the tool function.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
python/packages/core/agent_framework/_tools.py	Preserve None argument values during argument parsing for invoke and _auto_invoke_function.
python/packages/core/tests/core/test_tools.py	New test asserting explicit None arguments survive invocation.