For years now I have been tripping over Nulls in my field values. I have read much documentation on this subject and cannot see the sense in how Nulls are handled in SQL Server. Current rules include Null does not equal Null. Also, while Null certainly does not equal 'Y', the query engine does not see it that way.
I realize that Null is an unassigned value or an unknown value, but that does not mean that Null cannot equal Null. In the human world if a field on a piece of paper does not have anything in it, and another field on a piece of paper does not have anything it in they are both Null, and consequently are the same value, unknown/unassigned. As humans we would state that they are the same thing, blank.