private Iterable<List<Object>> buildCartesianProduct(Set<?>... sets) {
 List<Set<Optional<?>>> optionalSets = Lists.newArrayListWithExpectedSize(sets.length);
 for (Set<?> set : sets) {
  Set<Optional<?>> optionalSet =
    Sets.newLinkedHashSet(Iterables.transform(set, NULLABLE_TO_OPTIONAL));
  optionalSets.add(optionalSet);
 }
 Set<List<Optional<?>>> cartesianProduct = Sets.cartesianProduct(optionalSets);
 return Iterables.transform(
   cartesianProduct,
   new Function<List<Optional<?>>, List<Object>>() {
    @Override
    public List<Object> apply(List<Optional<?>> objs) {
     return Lists.transform(objs, OPTIONAL_TO_NULLABLE);
    }
   });
}