sp_helpDB give you error

Some times when you try to use sp_helpDB you may get the following problem. It can result in your database even not backuped up.

Server: Msg 515, Level 16, State 2, Procedure sp_helpdb, Line 53
Cannot insert the value NULL into column '', table ''; column does not allow nulls. INSERT fails.

This error might be because your database have an invalid owner. You can identify the databases with this issue using the followng script.
use master
go
SELECT name, SUSER_SNAME(sid) FROM sysdatabases WHERE SUSER_SNAME(sid) IS NULL.

The above statement will produce databases with invalid database owner. You can fix this by running the following system stored procedure. To fix this problem run sp_changedbowner 'sa'. You can replace sa with a vaild user.