jquery/jquery-ui — comment on commit b7df9e45cdce8846080528e31059700a9001b6f0
File: ui/jquery.ui.selectmenu.js line 146
By fnagel:

So its about how to handle an empty select tag. Which leads to the question how to handle empty options or even empty optgroups.
I fixed this problem and in general handling of empty tags. Empty oprgroups wont be displayed atm.

Thanks for helping out!