Error in handling hue value in HSL color model

hslHueF says:
return ct.ahsl.hue == USHRT_MAX ? -1.0 : ct.ahsl.hue / 36000.0;
It thinks that for achromatic color hue should be set to USHRT_MAX. But function toHsl sets it to 0. As the result hslHueF returns 0 for achromatic colors, while is should return -1.