// type parameter <S> lets us avoid the extra <String> in statements like:
  // Ordering<String> o = Ordering.<String>natural().nullsLast();
  public <S extends T> Ordering<@Nullable S> nullsLast() {
    return new NullsLastOrdering<S>(this);
  }

  /**
   * Returns a new ordering on {@code F} which orders elements by first applying a function to them,