Reverse-gradient will cause errors in future versions of Sass

[ry5n]

Since Sass 3.4.10 (January), passing anything other than a non-string value to the unquote function is deprecated and will be an error in future versions of Sass. This affects the reverse-gradient function, which (for some code paths) tries to pass a list through unquote.

We need to make sure any unquote calls are only ever passed strings, not lists.