* #headMap(Object, boolean)}. If you override {@code headMap}, you may wish to override {@code
   * lowerEntry} to forward to this implementation.
   */
  protected @Nullable Entry<K, V> standardLowerEntry(@ParametricNullness K key) {
    return headMap(key, false).lastEntry();
  }

  @Override
  public @Nullable K lowerKey(@ParametricNullness K key) {
    return delegate().lowerKey(key);
  }

  /**

   * #headMap(Object, boolean)}. If you override {@code headMap}, you may wish to override {@code
   * lowerEntry} to forward to this implementation.
   */
  protected @Nullable Entry<K, V> standardLowerEntry(@ParametricNullness K key) {
    return headMap(key, false).lastEntry();
  }

  @Override
  public @Nullable K lowerKey(@ParametricNullness K key) {
    return delegate().lowerKey(key);
  }

  /**