Fix unreachable response_format default in JudgeLM

[oraziooztas]

What does this PR do?

Fixes a conditional in JudgeLM.__init__ that never applies the intended default:

self.response_format = response_format if not None else DEFAULT_FORMAT

The condition evaluates the constant expression not None (always True), so:

• DEFAULT_FORMAT = {"type": "text"} (line 46) is unreachable dead code;
• when response_format is not provided, None is stored and forwarded as-is to the backend request kwargs (litellm kwargs and the OpenAI/TGI chat.completions calls), instead of the documented text-format default.

The fix tests the variable, as intended:

self.response_format = response_format if response_format is not None else DEFAULT_FORMAT

Tests

Added tests/unit/metrics/test_llm_as_judge_response_format.py:

• test_response_format_defaults_when_not_provided — fails on main (response_format stays None), passes with this fix;
• test_explicit_response_format_is_preserved — guards against regressing the explicit-format path.

No network, no external dependencies (pure __init__ behavior). ruff check and ruff format --check pass on both changed files.

🤖 Generated with Claude Code

https://claude.ai/code/session_0158ZooCCJEy6xtme9c8iksT