macOS Binding Keypath Modifiers?

I've got a very simple binding that enables a NSPopUpButton. The binding is a BOOL value. However I want the NSPopUpButton to be enabled when the BOOL value is false. Are there such a thing as keypath modifiers? Kinda like NSArray's @count, @max etc?

I've searched everywhere but am obviously calling it the wrong name if it does exist.

Thanks for your help.

Edit:
I'd like something like
@not.isDisplayed

Ahh yes! I knew this one wouldn't slip by you kainjow, thank you!