Thank you. By combining ISNULL and NULLIF functions it's the most elegant handling of the true NULL and text NULL scenario I've seen. Few months back I was doing it using AND, which made for very long statement. This is better.
WHEN ISNULL(NULLIF(realname, 'NULL'), '') = '' AND ISNULL(NULLIF(computer_name, 'NULL'), '') = '' then email
--Quote me