MemberMaybeNullAttribute

[NN---]

There is MaybeNullAttribute which can be applied to the parameter.
However there is counterpart for members.

I propose adding MemberMaybeNullAttribute which means the member might have null value.
This is the opposite of MemberNotNullAttribute.

Usage:
Suppose we have methods Set setting to a non null value and Clear setting null value.
I would like to tell compiler that this code has an issue:

Set()
Clear()
UseValue // here it is null