Error: content-exists() may only be called within a mixin.
  @return content-exists(); // must be called within a mixin
          ^^^^^^^^^^^^^^^^
  spec/sass_3_5/functions/content-exists/errors/inside-function/input.scss 2:11  my-content-exists()
  spec/sass_3_5/functions/content-exists/errors/inside-function/input.scss 7:12  uses-content-exists-indirectly()
  spec/sass_3_5/functions/content-exists/errors/inside-function/input.scss 14:1  root stylesheet
