}

  @Override
  public boolean equals(@Nullable Object object) {
    if (object == this) {
      return true;
    }
    if (object instanceof NullsFirstOrdering) {
      NullsFirstOrdering<?> that = (NullsFirstOrdering<?>) object;
      return this.ordering.equals(that.ordering);
    }
    return false;
  }

  @Override
  public int hashCode() {

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

  /**
   * Returns an ordering that treats {@code null} as greater than all other values and uses this
   * ordering to compare non-null values.
   *