Not equal to NULL and not equal to zero

I'm trying to accomplish the same thing and what occurs to me after reading this is to attach an action so that if the user even clicks on an unacceptable blank it assigns that blank's variable as Done. Then, you can add to the advanced action that if "unwanted blank" = Done it marks it wrong. If ≠ Done marks it right. I'll see if that works for me.

The variable v_null appeared in one of my blog posts 9 years ago, see that it has been taken over by many. That post has been updated recently:

http://blog.lilybiri.com/where-is-null-in-cp2017

Can you explain exactly what you want to do? Normally the logical expression with 'equal to v_null' should work.