I think there are a few pieces of important things to consider here, the first may be the way you're searching.
Hide / Unhide leads me to eyes and eyes crossed off very similar to user19969 response
But, what it sounds like you're actually after is more of
Collapse / Show or
Collapse / Display which leads to some results similar to Chairman Meow. In fact that image was the first one I found on a Google search for
expand collapse icons.
I think the difference is that based on what you wrote my understanding is you have something like this:
And you want a single set of icons that would remove/hide/collapse the Cats and Cars since those two are empty.
If this is correct I think it should be migrated back to UX because I think you should have some sort of text along with an icon. Something probably on the side that says, "Hide Empty Categories" or something of that nature. Otherwise you'll need an icon by each of those columns and that will get very messy because you're not saying to hide the list but keep the heading, my understanding at least is that you want to hide the heading as well. So... what would the icon be next to when its invisible?