return (row == null) ? null : safeGet(row, columnKey);
  }

  @Override
  public boolean isEmpty() {
    return size() == 0;
  }

  @Override
  public void clear() {
    Iterators.clear(cellSet().iterator());
  }

  @CanIgnoreReturnValue
  @Override
  public @Nullable V remove(@Nullable Object rowKey, @Nullable Object columnKey) {
    Map<C, V> row = safeGet(rowMap(), rowKey);

          @Override
          public Iterator<Entry<Range<K>, V>> iterator() {
            return entryIterator();
          }

          @Override
          public boolean retainAll(Collection<?> c) {
            return removeEntryIf(not(in(c)));
          }

          @Override
          public int size() {
            return Iterators.size(iterator());
          }

          @Override

    Iterator<String> iterator = asList("a", "b", "a").iterator();
    Multiset<String> multiset = ImmutableMultiset.copyOf(iterator);
    assertEquals(HashMultiset.create(asList("a", "b", "a")), multiset);
  }

  public void testCopyOf_iteratorContainingNull() {
    Iterator<@Nullable String> iterator =
        Arrays.<@Nullable String>asList("a", null, "b").iterator();
    assertThrows(

 * order of the various views.
 *
 * <p>The views returned by {@link #column}, {@link #columnKeySet()}, and {@link #columnMap()} have
 * iterators that don't support {@code remove()}. Otherwise, all optional operations are supported.
 * Null row keys, columns keys, and values are not supported.
 *

 * order of the various views.
 *
 * <p>The views returned by {@link #column}, {@link #columnKeySet()}, and {@link #columnMap()} have
 * iterators that don't support {@code remove()}. Otherwise, all optional operations are supported.
 * Null row keys, columns keys, and values are not supported.
 *

  }

  public void testCopyOf_iterator_general() {
    Iterator<String> iterator = asList("a", "b", "a").iterator();
    Multiset<String> multiset = ImmutableSortedMultiset.copyOf(iterator);
    assertEquals(HashMultiset.create(asList("a", "b", "a")), multiset);
  }

  public void testCopyOf_iteratorContainingNull() {
    Iterator<String> iterator = asList("a", null, "b").iterator();

    return (row == null) ? null : safeGet(row, columnKey);
  }

  @Override
  public boolean isEmpty() {
    return size() == 0;
  }

  @Override
  public void clear() {
    Iterators.clear(cellSet().iterator());
  }

  @CanIgnoreReturnValue
  @Override
  public @Nullable V remove(@Nullable Object rowKey, @Nullable Object columnKey) {
    Map<C, V> row = safeGet(rowMap(), rowKey);

 *   <li>{@link ContiguousSet}
 * </ul>
 *
 * <h2>Classes of static utility methods</h2>
 *
 * <ul>
 *   <li>{@link Collections2}
 *   <li>{@link Comparators}
 *   <li>{@link Iterables}
 *   <li>{@link Iterators}
 *   <li>{@link Lists}
 *   <li>{@link Maps}
 *   <li>{@link MoreCollectors}
 *   <li>{@link Multimaps}
 *   <li>{@link Multisets}
 *   <li>{@link ObjectArrays}
 *   <li>{@link Queues}
 *   <li>{@link Sets}

  public final void clear() {
    backingMap.clear();
    size = 0;
  }

  /**
   * Skeleton of per-entry iterators. We could push this down and win a few bytes, but it's complex
   * enough it's not especially worth it.
   */
  abstract class Itr<T extends @Nullable Object> implements Iterator<T> {
    int entryIndex = backingMap.firstIndex();
    int toRemove = -1;
    int expectedModCount = backingMap.modCount;

      assertThat(collection.isEmpty()).isTrue();
    }
    assertThat(Iterables.size(collection)).isEqualTo(size);
    assertThat(Iterators.size(collection.iterator())).isEqualTo(size);
  }