rules forms support: unable to check if no values are selected

I would love to know that to!
I tried with '' and 0 and NULL , and all "levels" of form ids but none of this work...

In the meantime you can do still it with the action "Execute PHP code" and something like:

return empty($form['field_ref']['0']['value']);

Cheers!

Perhaps there can be a backport.

Have you tried leaving the value empty, but checking the "negate" checkbox? That works for me. Now, if I could only work out how to make it work for checkbox input types.

Sorry, I just realised I didn't really answer your question. The negate option may be helpful anyway.

This is a valid feature that I've already implemented on a site I support. I'll be moving that feature here.

Commited on 7.x-1.x