* {@link #lowerEntry}, you may wish to override {@code lowerKey} to forward to this
   * implementation.
   */
  protected @Nullable K standardLowerKey(@ParametricNullness K key) {
    return keyOrNull(lowerEntry(key));
  }

  @Override
  public @Nullable Entry<K, V> floorEntry(@ParametricNullness K key) {
    return delegate().floorEntry(key);
  }

   * {@link #lowerEntry}, you may wish to override {@code lowerKey} to forward to this
   * implementation.
   */
  protected @Nullable K standardLowerKey(@ParametricNullness K key) {
    return keyOrNull(lowerEntry(key));
  }

  @Override
  public @Nullable Entry<K, V> floorEntry(@ParametricNullness K key) {
    return delegate().floorEntry(key);
  }