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

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

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

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