smart album

In Aperture 3.1.2 I was able to create a smart album where it automatically put all the photos that were not yet assigned to any regular album. Doing this: in the HUD I selected Add Rule Aperture Metadata, thenselect Album Name empty and everything worked.

Now I am not able to create the same smart album in Aperture 3.4.3

What has happened? Something has changed in the new version so this type of smart album has to be created in a different way?

Thank for help,

Claudio