return (SortedMap<K, V>) super.entriesOnlyOnRight();
    }
  }

  /**
   * Returns the specified comparator if not null; otherwise returns {@code Ordering.natural()}.
   * This method is an abomination of generics; the only purpose of this method is to contain the
   * ugly type-casting in one place.
   */
  @SuppressWarnings("unchecked")
  static <E extends @Nullable Object> Comparator<? super E> orNaturalOrder(