This is why writers like Chris Date take great pains to explain that "null value" is an oxymoron. Null is a "mark", not a value -- it exists entirely apart fro

This is why writers like Chris Date take great pains to explain that "null value" is an oxymoron. Null is a "mark", not a value -- it exists entirely apart from any domain. Any language or environment that doesn't respect this abuses the entire concept.