@SuppressWarnings({"unchecked", "rawtypes"}) // TODO(kevinb): the right way to explain this??
@ElementTypesAreNonnullByDefault
final class ReverseNaturalOrdering extends Ordering<Comparable<?>> implements Serializable {
  static final ReverseNaturalOrdering INSTANCE = new ReverseNaturalOrdering();

  @Override
  public int compare(Comparable<?> left, Comparable<?> right) {
    checkNotNull(left); // right null is caught later

      result = nullsLast = super.<Comparable<?>>nullsLast();
    }
    return (Ordering<@Nullable S>) result;
  }

  @Override
  public <S extends Comparable<?>> Ordering<S> reverse() {
    return (Ordering<S>) ReverseNaturalOrdering.INSTANCE;
  }

  // preserving singleton-ness gives equals()/hashCode() for free
  private Object readResolve() {
    return INSTANCE;
  }

  @Override
  public String toString() {