ComPy

Hello I took over an existing processwire project and had to develop a custom fieldtype. It was more like adjust and existing fieldtype. Everything seems to work fine but it doesnt work like the other fields when I select the option Open when populated + Closed when blank. It'll stay always open. Even if the inputs are empty. If I set it to closed it will be closed. So I guess the field doesnt recognize it is blank. Couldnt figure out how it determines blank fields. Tried to set DB NULL, 0, empty with no luck. Any help where the cms checks fields state?