* #tailMap(Object, boolean)}. If you override {@code tailMap}, you may wish to override {@code
   * ceilingEntry} to forward to this implementation.
   */
  protected @Nullable Entry<K, V> standardCeilingEntry(@ParametricNullness K key) {
    return tailMap(key, true).firstEntry();
  }

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

   * #tailMap(Object, boolean)}. If you override {@code tailMap}, you may wish to override {@code
   * ceilingEntry} to forward to this implementation.
   */
  protected @Nullable Entry<K, V> standardCeilingEntry(@ParametricNullness K key) {
    return tailMap(key, true).firstEntry();
  }

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