Null value in user mapping leads to "Unknown Users"

Summary:

• Confluence 5.4.3
• PostgreSQL 8.4.13

An entry in the user_mapping table has a null value for the lower_username field, which causes users to be shown as 'unknown user' when searching.

Your database may look like this:

             user_key             |         username         |      lower_username      
----------------------------------+--------------------------+--------------------------
 ff808081407d63f001407d643c890515 | rprice                   | rprice
 ff808081407d63f001407d643a70018f | rprice                   | 
 ff808081407d63f001407d6439df0079 | rcummins                 | rcummins
 ff808081407d63f001407d643a370125 | rcummins                 | 

Resolution:

Remove the user mappings with null values from the database. See CONF-36018 for the set of SQL queries to achieve this.

Avoiding this in the future:

Is it possible to add a constraint to lower_username to prevent null values?