*/
  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() {

        Iterator<Entry<K, V>> entryIterator = backingMap.entrySet().iterator();

        return new UnmodifiableIterator<K>() {
          @Override
          public boolean hasNext() {
            return entryIterator.hasNext();
          }

          @Override
          public K next() {
            Entry<K, V> entry = entryIterator.next(); // store local reference for thread-safety

  }

  @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() {

   */
  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() {

    Iterator<Entry<String, Integer>> entryIterator = multimap.entries().iterator();
    assertEquals(immutableEntry("foo", 5), entryIterator.next());
    assertEquals(immutableEntry("bar", 4), entryIterator.next());
    assertEquals(immutableEntry("foo", 3), entryIterator.next());
    assertEquals(immutableEntry("cow", 2), entryIterator.next());
    assertEquals(immutableEntry("bar", 1), entryIterator.next());

   */
  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;

      lastEntry = null;
    }
  }

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

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

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

    @Override

    Entry<String, String> firstEntry = entries.iterator().next();
    entries.remove(firstEntry);
    assertFalse(underlying.containsKey("f"));

    Iterator<Entry<String, String>> entryIterator = entries.iterator();
    entryIterator.next();
    entryIterator.remove();
    assertFalse(underlying.containsKey("g"));

    assertTrue(underlying.isEmpty());
    assertTrue(map.isEmpty());
    assertTrue(keys.isEmpty());