[at_a_remove]

I have deep but vague thoughts around the concept. My first intuition is that we have put too many things under NULL and None and such.

Partially, we use ... and I'll be very broad here ... "variables" as boxes we look in for answers. Answers to questions, answers to "Hey I put something in there for the time being to reference later." If I went into programming terms rather than just SQL, sometimes we get meta-answers.

You haven't made the box yet (declared the variable).

You haven't decided how the box is structured (picked a type or a length or something).

Okay, you did those but the box is virgin (nothing has been placed in the box yet).

That kind of thing. An empty set for "yes, you asked but nothing meets those criteria."