*scale = *Sub::Nary::scale{CODE};
-is_deeply(scale(1, {}), { 0 => 1 }, 'scale 1, empty-ref');
-is_deeply(scale(0.5, {}), { 0 => 0.5 }, 'scale 0.5, empty-ref');
+is_deeply(scale(1, {}), undef, 'scale 1, empty-ref');
+is_deeply(scale(0.5, {}), undef, 'scale 0.5, empty-ref');
is_deeply(scale(0.5, { list => 2 }), { list => 1 }, 'scale 0.5, list');
is_deeply(scale(0.5, { list => 2, 1 => 2 }), { list => 1, 1 => 1 },
'scale 0.5, list/const');