How to not show tooltip for some TreeView items?

We don’t want tooltips for TreeView items that contain other items, but when I return an empty String for those items, the tooltip still shows, just as a small black square (with what appears to be little colored corners). How do I not show a tooltip at all for selected items? These items are folder names in a file/folder hierarchy, and because they are not files, they cannot contain the information we need to specify a tooltip. The only solution I have thought of so far is to show the folder name both in the TreeView and in the tooltip, but that’s a little redundant.

I tried overriding drawTooltip in our LookAndFeel class, and not doing anything at all there if the text is empty, but that function doesn’t seem to be called at all!?!