}

  @Override
  public @Nullable Entry<E> firstEntry() {
    Iterator<Entry<E>> entryIterator = entryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  public @Nullable Entry<E> lastEntry() {
    Iterator<Entry<E>> entryIterator = descendingEntryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  public @Nullable Entry<E> pollFirstEntry() {

  }

  @Override
  public @Nullable Entry<E> firstEntry() {
    Iterator<Entry<E>> entryIterator = entryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  public @Nullable Entry<E> lastEntry() {
    Iterator<Entry<E>> entryIterator = descendingEntryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  public @Nullable Entry<E> pollFirstEntry() {

  }

  @Override
  public @Nullable Entry<E> firstEntry() {
    Iterator<Entry<E>> entryIterator = entryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  public @Nullable Entry<E> lastEntry() {
    Iterator<Entry<E>> entryIterator = descendingEntryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  public @Nullable Entry<E> pollFirstEntry() {

      lastEntry = null;
    }
  }

  /** KeyIterator build on top of EntryIterator. */
  final class KeyIterator implements Iterator<K> {
    private final EntryIterator iterator;

    KeyIterator() {
      iterator = new EntryIterator();
    }

    @Override
    public boolean hasNext() {
      return iterator.hasNext();
    }

    @Override

import java.util.NavigableSet;
import java.util.Set;
import org.jspecify.annotations.Nullable;

/**
 * A skeleton implementation of a descending multiset. Only needs {@code forwardMultiset()} and
 * {@code entryIterator()}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
abstract class DescendingMultiset<E extends @Nullable Object> extends ForwardingMultiset<E>
    implements SortedMultiset<E> {

    public boolean equals(@Nullable Object obj) {
      return Sets.equalsImpl(this, obj);
    }
  }

  abstract Iterator<Entry<K, V>> entryIterator();

  Spliterator<Entry<K, V>> entrySpliterator() {
    return Spliterators.spliterator(
        entryIterator(), size(), (this instanceof SetMultimap) ? Spliterator.DISTINCT : 0);
  }

  @LazyInit private transient @Nullable Set<K> keySet;

  @Override

   */
  protected @Nullable Entry<E> standardPollFirstEntry() {
    Iterator<Entry<E>> entryIterator = entrySet().iterator();
    if (!entryIterator.hasNext()) {
      return null;
    }
    Entry<E> entry = entryIterator.next();
    entry = Multisets.immutableEntry(entry.getElement(), entry.getCount());
    entryIterator.remove();
    return entry;
  }

  @Override
  public @Nullable Entry<E> pollLastEntry() {

    // Avoiding ConcurrentModificationExceptions is tricky.
    Iterator<Entry<E>> entryIterator = multisetToModify.entrySet().iterator();
    boolean changed = false;
    while (entryIterator.hasNext()) {
      Entry<E> entry = entryIterator.next();
      int retainCount = occurrencesToRetain.count(entry.getElement());
      if (retainCount == 0) {
        entryIterator.remove();
        changed = true;

    // Avoiding ConcurrentModificationExceptions is tricky.
    Iterator<Entry<E>> entryIterator = multisetToModify.entrySet().iterator();
    boolean changed = false;
    while (entryIterator.hasNext()) {
      Entry<E> entry = entryIterator.next();
      int retainCount = occurrencesToRetain.count(entry.getElement());
      if (retainCount == 0) {
        entryIterator.remove();
        changed = true;

   */
  protected @Nullable Entry<E> standardPollFirstEntry() {
    Iterator<Entry<E>> entryIterator = entrySet().iterator();
    if (!entryIterator.hasNext()) {
      return null;
    }
    Entry<E> entry = entryIterator.next();
    entry = Multisets.immutableEntry(entry.getElement(), entry.getCount());
    entryIterator.remove();
    return entry;
  }

  @Override
  public @Nullable Entry<E> pollLastEntry() {