Python: Handle empty chat message function results

[Alperen (lprnmns)]

Motivation and Context

FunctionResultContent.from_function_call_content_and_result() raises IndexError when a tool returns a valid empty ChatMessageContent, because it reads result.items[0] before converting the message to text.

This is distinct from #14359 / #14364, which handle an empty string passed through ChatHistory.add_tool_message(); that change does not affect this factory path.

Description

Remove the item inspection from the ChatMessageContent branch. Those extracted values were immediately overwritten by str(result), so non-empty behavior is unchanged while an empty message now becomes an empty function result. A focused regression covers the empty result and retained inner_content.

Validation

• uv run pytest -q tests/unit/contents/test_function_result_content.py --maxfail=1
• uv run pytest -q tests/unit/contents/test_chat_history.py tests/unit/kernel/test_kernel.py --maxfail=1
• uv run pytest -q tests/unit/contents --maxfail=1
• uv run pre-commit run --files semantic_kernel/contents/function_result_content.py tests/unit/contents/test_function_result_content.py
• git diff --check

The complete Python unit suite was attempted but could not collect because the optional autogen extra is not installed; all relevant and package-level contents tests passed.

This is backward compatible and changes no public API.

[Copilot]

🟢 Approval recommended

The change is small, targeted to the reported IndexError, and includes a focused regression test covering the boundary case.

Pull request overview

This PR fixes a Python edge case where FunctionResultContent.from_function_call_content_and_result() could raise IndexError when a tool returned a valid but empty ChatMessageContent, by avoiding unsafe items[0] access and adding a regression test to lock in the behavior.

Changes:

• Remove ChatMessageContent.items[0] inspection in from_function_call_content_and_result() to prevent IndexError on empty messages.
• Add a focused unit test asserting empty ChatMessageContent results become an empty function result while preserving inner_content.

File summaries

File	Description
python/semantic_kernel/contents/function_result_content.py	Removes unsafe items[0] access in the ChatMessageContent conversion path to avoid IndexError for empty tool messages.
python/tests/unit/contents/test_function_result_content.py	Adds a regression test covering empty ChatMessageContent results and inner_content retention.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Lite

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[github-actions]

MAF Automated Review — Iteration 1

Result: No findings
Scope: full PR (1 commit(s)): dd0092796566
Model: claude-opus-4.8

Overview

The PR removes an item-inspection block from the ChatMessageContent branch of
FunctionResultContent.from_function_call_content_and_result() and lets res = str(result) stand alone, fixing an IndexError raised when a tool returns a
ChatMessageContent with an empty items list. The removed assignments were
provably dead code — each res = result.items[0]... was unconditionally
overwritten by the following res = str(result) line — so every non-empty input
produces byte-identical output before and after the change. The only observable
behavioral delta is that an empty message now yields an empty-string result
instead of crashing, which is confirmed by the added regression test and does not
cross or weaken any trust boundary. No public API, serialization, or provider
parity regression was found.

Reviewed the supplied pull-request change set across correctness, security/reliability, architecture, and failure behavior.
No publishable findings remained after source verification for this scope.

[Alperen (lprnmns)]

@microsoft-github-policy-service agree