ActionImpl.unitCommand with empty List/Set as parameter

[Ketroc]

It would be a nice quality of life change to have unitCommand() do nothing if given an empty unit List/Set as a parameter. Since these lists are almost always generated in a way where they could be empty, we currently have to do an empty check or error handling for every unitCommand() call.

[Supalosa]

+1 - if no objection i could add this.