}

  @Override
  @CheckForNull
  public Entry<K, V> floorEntry(K key) {
    return headMap(key, true).lastEntry();
  }

  @Override
  @CheckForNull
  public K floorKey(K key) {
    return keyOrNull(floorEntry(key));
  }

  @Override
  @CheckForNull
  public Entry<K, V> ceilingEntry(K key) {
    return tailMap(key, true).firstEntry();
  }

  @Override