sub func {
   my ($error) = @_;
   my @results = ('some', 'values');   # 1 or more values.
   $error ? () : @results;
}

for (0..1) {
   my @results = func($_);
   print(@results ? "no error (@results)" : 'error', "\n");
}

##</code><code>##

sub func {
   my ($error) = @_;
   my @results = ();                   # 0 or more values.
   $error ? undef : \@results;
}

for (0..1) {
   my $results = func($_);
   print($results ? "no error (@$results)" : 'error', "\n");
}