NULLs in SQL are a mess so I don't think one should try to attach any general meaning to them. Nor should SQL's NULL handling be a model for any other language.

NULLs in SQL are a mess so I don't think one should try to attach any general meaning to them. Nor should SQL's NULL handling be a model for any other language. For example, 1+NULL is NULL, but adding the same two values via SUM(1, NULL), returns 1.