In the "Available Package Updates" portion of up2date, if the user clicks
the 'Next' button without any checked packages, a transient announces "You
must select at least one package."

This might be an issue when the user doesn't wish to update anything, but
isn't sure what process the application is following, and is proceeding in
case there's more to be done.  A clearer message would be something along
the lines of "You must select one package.  If you do not wish to update
any packages, press the 'Cancel' button to exit the Update Agent."