Much like I suggested in my Empty Date Field post, I’ve found myself starting to add EmptyName as a column to some of my lists that require comparisons (usually during workflows) to blank values. I just find it easier to know I’m going to match up exactly to what a blank people picker field will look like.
Just create a column in the list, name it something like EmptyName, and leave the default value as blank. Then use that field as the comparison value to any of your other names that you’d like to check against.
SharePoint Duffbert 