https://github.com/jsdom/cssstyle/blob/4533e6f35305dd154d693534fb4cf01dacdb72e9/lib/parsers.js#L268 In `parseColor` we test if value is empty string or null, otherwise we continue to use `resolveColor`: ```js if (type === exports.TYPES.NULL_OR_EMPTY_STR) { return val; } if (/^[a-z]+$/i.test(val) && type === exports.TYPES.COLOR) { return val; } var res = resolveColor(val, { format: 'specifiedValue', }); ``` If `val` is undefined, this will cause an error in `resolveColor` We can prevent this by adding a test for undefined: ```js if (typeof val === undefined || type === exports.TYPES.NULL_OR_EMPTY_STR) { return val; } ```