[Bugfix] Fix forced tool_choice crash when reasoning_parser consumes all content

[FutureSkyFly]

Summary

When using --reasoning-parser (e.g., glm45, deepseek_r1) with forced tool_choice, the reasoning parser may consume the entire model output into <think>...</think> tags, leaving content as None. This causes AssertionError crashes in the forced tool_choice code paths.

Fix: Normalize None content to empty string "" (consistent with the existing "required" branch which already does content = content or ""), and replace the downstream assert tool_calls with a defensive fallback.

Changes

File	Change
vllm/entrypoints/openai/engine/serving.py	Replace 2x assert content is not None → content = content or ""
vllm/parser/abstract_parser.py	Replace 2x assert content is not None → content = content or ""
vllm/entrypoints/openai/chat_completion/serving.py	Replace assert tool_calls is not None and len(tool_calls) > 0 → tool_calls = tool_calls or []

Total: 5 lines changed across 3 files.

How to reproduce

vllm serve <reasoning-model> --reasoning-parser glm45 --enable-auto-tool-choice --tool-call-parser hermes

response = client.chat.completions.create(
    model="<model>",
    messages=[{"role": "user", "content": "What's the weather?"}],
    tools=[{"type": "function", "function": {"name": "get_weather", "parameters": {}}}],
    tool_choice={"type": "function", "function": {"name": "get_weather"}}
)
# Crash: AssertionError (no message) when model output is all <think>...</think>

Why this is not a duplicate

PR #40148 fixes engine/serving.py and abstract_parser.py but does not fix the downstream assert in chat_completion/serving.py (line 1417). This PR covers all 5 crash points across all 3 files.

Fixes #40528
Related: #40147, #40148

Test

The fix is consistent with the existing "required" branch pattern which already uses content = content or "" and tool_calls = tool_calls or [].

AI Disclosure

AI assistance was used in identifying and fixing this bug.

Signed-off-by: liuchenbing liuchenbing2026@outlook.com

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

[gemini-code-assist]

Code Review

This pull request replaces several assert statements with default value assignments in the OpenAI chat completion serving, engine serving, and abstract parser modules. Specifically, it ensures that tool_calls defaults to an empty list and content defaults to an empty string when they are None, preventing potential assertion errors and improving robustness. I have no feedback to provide.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @liuchen2026fly.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork