[reshlo]

> If your signup form has an optional field for middle name which I don’t fill, it can absolutely be because I don’t have a middle name.

The fact that some NULLs are indeed undefined doesn’t contradict my point that it would be inaccurate to refer to all NULLs as UNDEFINED.

> It’s undefined and known to be so… And because four value logic was left out, nulls have to fulfil multiple incompatible roles, and ends up being weird.

You know it to be undefined, but if you just leave that field blank on the form, the database still can’t know whether that’s because you don’t have one or because you didn’t provide the one you have, unless there was a field on the form that allowed you to explicitly indicate that you don’t have one.