there is no anon user name (that is meaningful, even if we have a constant one). That is, username is the PK of the field of (login-able) users, and one of those users could have the username "anonymous" and nothing could/should break, because we never attempt to lookup the ANON principle by username. You can never check if a username represents the anon user. Null username == "no one" or "anon user"