[paolo-perrone]

What does the PR do?

If a chat request forces a tool that has no "parameters" field, the OpenAI frontend returns a 500. OpenAI lets you leave "parameters" out for a function that takes no arguments, and our schema allows it too (FunctionObject.parameters is Optional), but _get_guided_json_from_tool calls tool.parameters.model_dump_json() without checking for None. Both the vLLM and the TRT-LLM request converters call it, so this hits every backend.

Repro: tools=[{"type": "function", "function": {"name": "get_current_time"}}] with tool_choice={"type": "function", "function": {"name": "get_current_time"}} (or tool_choice="required"). The response is a 500 with 'NoneType' object has no attribute 'model_dump_json'.

The fix returns an empty object schema, {"type": "object", "properties": {}}, when parameters is missing, so the forced call comes back with {} as its arguments. That's the same thing vLLM does for "required" when a tool has no parameters.

Checklist

• I have read the Contribution guidelines and signed the Contributor License Agreement (CLA is being sent to triton-cla@nvidia.com)
• PR title reflects the change and is of format <commit_type>: <Title>
• Changes are described in the pull request.
• Added test plan and verified test passes.
• I ran pre-commit locally
• Verified copyright is correct on all changed files.

Commit Type:

• fix

Where should the reviewer start?

python/openai/openai_frontend/engine/utils/triton.py, _get_guided_json_from_tool.

Test plan:

Added test_guided_json_for_tool_without_parameters to tests/test_tool_calling.py. It covers a named tool_choice and "required" with a tool that has no parameters. It fails on main with the AttributeError and passes with the fix. Tools that do have parameters get exactly the same schema as before.

Caveats:

Another option is to return None and skip guided decoding for these tools, which is what vLLM does for a named tool_choice. I went with the empty object schema so the arguments always come back as valid JSON. Happy to switch if you'd rather.

pre-commit's flake8 flags three existing lines in the same file (!= True twice and an unused except ... as e), which this PR doesn't touch. I left them alone to keep this to one change.

[greptile-apps]

Confidence Score: 5/5

[Medium impact] The PR appears safe to merge; the previous finding is fixed and no new actionable issues remain.

Summary

Fixes forced tool calls when a function omits parameters.

• Forced calls to tools without parameters now use an empty-object schema.

_{Reviews (2) · Last reviewed commit: "fix: Forbid extra keys in the no-paramet..." · Reviewed by Greptile}

[yinggeh]

LGTM. Please respond to the review comment.