InfoPath Dev

I've spent way to much time researching this and trying different things, time to ask the experts! I have a cascading drop-down in my InfoPath form. Works perfectly except for one thing. If there is no option, the drop-down still shows but it is empty. I want to hide it if it is empty and I can't get it to work. See attachment for table example. So if someone chooses Social Engineering > Vishing, Category 3 fields shows up blank. I would like it to not show since it is empty. Thank you!

 You have to add conditional formatting to the dropdown that checks to see if the node in the secondary data source that provides the value is blank when the other data items match - see attached sample for an idea. Save the sample locally, right click & select Design, then you can preview / look at the formulas.