Production Surprise

I found this while I was debugging a minor production problem this afternoon.

if (userName.Contains(""))
userName = GetUserName(userName);
 
if (String.IsNullOrEmpty(userName))
throw new ArgumentNullException("userName can not be null. Verify identity.Name is not empty.");

This code was written last month during a refactor of this method, and I can not for the life of me understand what userName.Contains(“”) is there for. [...]