Indication of null variables

A check is something, an empty checkbox is missing something.
HasValue is therefore my favourite.

Whether it's subconscious or not, you might have told us your own opinion by your numbering.

Hi,

on entry I would use a checkbox, checked==hasValue, and a TextBox or something like that, which
gets empty&&disabled or invisible on !hasValue

on display, I would use a TextBox that shows the value when hasValue, and gets both empty and
grayed when !hasValue

but then I am not sure you always need a checkbox, your control (say a TextBox) may have a
no-value indication anyhow (say a number in a TextBox, an empty TextBox would be !hasValue).
So I would only use the checkbox if the value can be present but invisible (as in an empty string).

:)