[rupayon123]

ArgvInput.parameter_option("--name", default="fallback") returns False when no token matches. Its existing end-of-options branch already returns the supplied default.

Return that default after an exhausted scan too. Tests cover empty and unrelated tokens, single/list option names, False, 0, None, string and object defaults, plus present values and -- controls. The separate attached-value work in #538 is untouched.

Validation on macOS arm64/CPython 3.13.14 with dependencies from poetry.lock: 274 tests pass, three existing skips; mypy, all-file pre-commit checks, package build and built-wheel API checks pass. The inherited NO_COLOR=1 environment triggers the same existing FORCE_COLOR test failure on the pristine base; the passing full run unsets that inherited variable. Other Python/OS combinations were not run locally.

Includes the required news/549.bugfix.md changelog entry.

[agammann]

I checked both absence paths in parameter_option: reaching -- with only_params=True already returned the caller’s default, but exhausting _tokens returned False. This change makes those paths consistent while preserving False for callers that omit the argument. The added cases also check 0, None, and an object by identity, so falsy or sentinel defaults are not accidentally replaced; the present-option and -- controls cover the surrounding behavior. I reviewed the diff and method; I did not run tests locally.