* {@code higherEntry}, you may wish to override {@code higherKey} to forward to this
   * implementation.
   */
  protected @Nullable K standardHigherKey(@ParametricNullness K key) {
    return keyOrNull(higherEntry(key));
  }

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

  /**

   * {@code higherEntry}, you may wish to override {@code higherKey} to forward to this
   * implementation.
   */
  protected @Nullable K standardHigherKey(@ParametricNullness K key) {
    return keyOrNull(higherEntry(key));
  }

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

  /**