views_handler_field_user_name does not handle NULL columns

Problem

1. I have an entity type which has an optional user reference property (name uid, type integer).
2. Entity API adds the relationship handler to said field so we can left join the {users} table.
3. Upon left joining, I have some rows with an empty uid
4. Using the "User: Name" field will return "Anonymous" instead of nothing

Cause

The field handler views_handler_field_user_name does not take into account that the UID may be NULL

Solution

Make the handler respect NULL values