Allow empty mixin
Allow empty mixin

This mixin might somday get some default list rules, for now it is ok
that it is empty.

dartajax/frontend,jrjohnson/frontend,dartajax/frontend,ilios/frontend,gabycampagna/frontend,ilios/frontend,jrjohnson/frontend,djvoa12/frontend,gabycampagna/frontend,djvoa12/frontend,thecoolestguy/frontend,gboushey/frontend,gboushey/frontend,thecoolestguy/frontend