sub build_list {
   my ($arg1, arg2, ...) = @_;
   my @list = ();
   ...
   if (something) {
      return @list;
   } else {
      return ();
   }
}

##</code><code>##

sub build_list {
    ...
    my @list = ();

    if ( something ) {
       push @list, $whatever, ...;
    }

    return @list;  # list could still be empty at this point
}