[Assign Widget] Have the respective Null*() option in the possible values list in the Value field

When using the Assign Widget,after filling the Variable field, in the Value field is displayed a list of several possible input/local/output variables, aggregate return field/records, session variables, etc. of the same type of the filled Variable field.

My Idea is to include also the respective NullIdentifier()/NullTextIdentifier()/NullDate()/etc. option in this suggestion list.