[spicysharkco]

to_string() appends the angle unit to an undefined hue:

Color('hsl(none 50% 50%)').to_string(none=True, angle='turn')
# 'hsl(noneturn 50 50)'

noneturn is not valid CSS, and Color() cannot read it back. The strings docs say undefined channels "can be displayed as none" on output, so the result should be hsl(none 50 50). rad and grad do the same, and so does color=True. deg has no suffix, so it was already correct.

angle was added in 6.1. I ran the example on every tag from 6.1 to 8.13.1 and all of them give the wrong result.

color_function adds the unit whether or not the value is NaN (serialize.py#L105). Color.__repr__ already leaves the unit off for NaN, and the fix does the same.

Test: pytest tests/test_api.py -k test_to_string_angle fails on main with 'hsl(nonerad 50 50)' != 'hsl(none 50 50)' and passes with the change.

[facelessuser]

Please add a note in the change log.

[spicysharkco]

Added a changelog entry under 8.13.2.

[facelessuser]

@gir-bot lgtm