What is NULL? Is NULL a space? Is NULL a NULL string?
NULL is unknown. If null is unknown then you can not do anything with null.
You can not perform any operation on null: Y := 5+UNKNOWN then Y=UNKNOWN
You can not compare null to anything: IF 5>UNKNOWN THEN … END IF. Well that will never evaluate to true because just don’t know.
This is part of what makes NULL so difficult to work with. NULL complicates logic. So just say no to null.