UI Script to Hide Columns Not Working

Hi all,

I've got a custom OWL, and I'd like to hide columns if there's no data in them. I found a thread on here with a script, which I've stuck in:

So as far as I can tell, if the value of said column (I've aligned the screens so you can see it in the data view) is nothing, the visibility is false; otherwise, it's set to true. But here's what I've got in ByDesign...

Clearly, Mon Drop is empty...but it's not hidden. Ideas?

Lewis