first round of Perl::Critic cleanups. Do not use return undef, use a bare return instead

lib/WebGUI/Group.pm

@@ -1024,7 +1024,7 @@ sub new {
         unless ($groupExists) {
             $self->{_session}->errorHandler->warn('WebGUI::Group->new called with a non-existant groupId:'
                 .'['.$self->{_groupId}.']');
-            return undef;
+            return;
         }
     }