Really looking for some agreement from the masses here. I have a form, and was trying to validate that when a choice field is empty/Null, then the control is invalid. So I set the formula to isNullorEmpty({self}). Seems pretty basic, right? But no, this didn't work... So then i tried {self}==""... This didn't work either. Then I tried {self}=="Please select a value...", which is the default text in the choice field when nothing selected. This still didn't work.

So, to test what the value in an empty choice field actually is, I placed a calculation field on the form and made it equal to the value of that choice field. To my disbeleif, it has another value... "**SelectValue**".

I went back to my validation formula, and set it to {self}=="**SelectValue**" and this worked!!!!

Some things about Nintex are just absolutely annoying, and illogical. This is just another one. But I hope that someone else finds this helpful.