Integers support both addition and multiplication and taking maximum and minimums, and a few other semi-group operations. Do you want to define different Null elements for all of them?
No, I don't want to define a representation for Null to all possible combinations of a set and a function/operation. That can be done by each developer if they see it fit and of the operations they want to have this.
But, for me, it makes sense to have a default representation for Null (that it is not automatically coerced—only if the developer explicitly asks for it) for one of the most common operations in that specific group.
