Also OR/AND can return non-null results even if NULL is one side of the operator:

    (NULL AND 0) gives 0
    (0 AND NULL) gives 0
    (NULL AND 1) gives NULL
    (1 AND NULL) gives NULL
    (NULL AND NULL) gives NULL
    (NULL OR 0) gives NULL
    (0 OR NULL) gives NULL
    (NULL OR 1) gives 1
    (1 OR NULL) gives 1
    (NULL OR NULL) gives NULL