Revisit NumericRangeValidator allow NULL values

Continuing the discussion from NumericRangeValidator allow NULL values:

We are not sure how to fix this and that’s why we cannot fix it

Is it not possible to add a simple bool parameter as proposed: AllowNull?
With default of false it would be backwards compatible.

Else, a custom validator could do it, but it actually belongs in the NumericRangeValidator since null is "valid" validation opt-in.

Everything we have to say about this has already been said in the other thread. There was no need to open a new one. Thus I will close this as well.