*
   * <p>If you override {@link #entrySet()}, you may wish to override {@link #pollFirstEntry()} to
   * forward to this implementation.
   */
  protected @Nullable Entry<E> standardPollFirstEntry() {
    Iterator<Entry<E>> entryIterator = entrySet().iterator();
    if (!entryIterator.hasNext()) {
      return null;
    }
    Entry<E> entry = entryIterator.next();

   *
   * <p>If you override {@link #entrySet()}, you may wish to override {@link #pollFirstEntry()} to
   * forward to this implementation.
   */
  protected @Nullable Entry<E> standardPollFirstEntry() {
    Iterator<Entry<E>> entryIterator = entrySet().iterator();
    if (!entryIterator.hasNext()) {
      return null;
    }
    Entry<E> entry = entryIterator.next();

     * loop. Instead, we test standardLastEntry manually below.
     */

    @Override
    public @Nullable Entry<K, V> pollFirstEntry() {
      return standardPollFirstEntry();
    }

    @Override
    public @Nullable Entry<K, V> pollLastEntry() {
      return standardPollLastEntry();
    }

    @Override
    public NavigableMap<K, V> descendingMap() {