Created by: ysds
The box-shadow() mixin has been changed to handle none with multiple arguments in #27972 and #28004, but it should be null instead of none.
This PR make the box-shadow() mixin allow null and drop support none with multiple args. And add warning message when used none with multiple arguments.
before: https://www.sassmeister.com/gist/bdf41c41937a614861a026169e39279e after: https://www.sassmeister.com/gist/56fdeffc72831664e546baf22f365cdf