return null;
  }

  /**
   * Returns true if this entry has no bucket links and can safely be reused as a terminal entry in
   * a bucket in another map.
   */
  boolean isReusable() {
    return true;
  }

  static class NonTerminalImmutableMapEntry<K, V> extends ImmutableMapEntry<K, V> {
    /*
     * Yes, we sometimes set nextInKeyBucket to null, even for this "non-terminal" entry. We don't