In mathematical sets, the null set, also called the empty set, is the set that does not contain anything. There is only one null set. This is because there is logically only one way that a set can contain nothing.
The null set makes it possible to explicitly define the results of operations on certain sets that would otherwise not be explicitly definable. The intersection of two disjoint sets (two sets that contain no elements in common) is the null set.
Seems to me this is a better description of the weapons of mass destruction alleged to be in Iraq that were also found in Iraq, or of the purported reasons for going to war in Iraq that were also true, than a justification for not answering a question about whether, knowing what we now know, we should have gone to war (or given W the authority to do so).
Just the sort of pompous, pretentious, arrogant, self-serving bullshit we need in our next President. If I want someone that pompous (without all the trailing adjectives), I'll take Al Gore, who at least often knows what he is talking about.
Oh, one more try on null sets: the number of people on that stage who also might make a decent President.