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

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

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

  @CanIgnoreReturnValue
  @Override
  @CheckForNull
  public V remove(@CheckForNull Object rowKey, @CheckForNull Object columnKey) {

  /**
   * This is a less carefully-controlled version of {@link #testRemovalNotification_clear} - this is
   * a black-box test that tries to create lots of different thread-interleavings, and asserts that
   * each computation is affected by a call to {@code clear()} (and therefore gets passed to the
   * removal listener), or else is not affected by the {@code clear()} (and therefore exists in the
   * cache afterward).
   */

    totalSize -= collection.size();
    collection.clear();

    return unmodifiableCollectionSubclass(output);
  }

  <E extends @Nullable Object> Collection<E> unmodifiableCollectionSubclass(
      Collection<E> collection) {
    return Collections.unmodifiableCollection(collection);
  }

  @Override
  public void clear() {
    // Clear each collection, to make previously returned collections empty.

 * https://github.com/google/guava/issues/3990
 */
@GwtIncompatible
@ElementTypesAreNonnullByDefault
final class Java8Compatibility {
  static void clear(Buffer b) {
    b.clear();
  }

  static void flip(Buffer b) {
    b.flip();
  }

  static void limit(Buffer b, int limit) {
    b.limit(limit);
  }

  static void position(Buffer b, int position) {

    assertEquals(expected, copyToList(sortedMultiset.entrySet()));
  }

  @CollectionSize.Require(SEVERAL)
  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testClearHeadOpen() {
    List<Entry<E>> expected =
        copyToList(sortedMultiset.tailMultiset(b.getElement(), CLOSED).entrySet());
    sortedMultiset.headMultiset(b.getElement(), OPEN).clear();

   * clear()} clears all table mappings.
   */
  @WeakOuter
  private abstract class TableSet<T> extends ImprovedAbstractSet<T> {
    @Override
    public boolean isEmpty() {
      return backingMap.isEmpty();
    }

    @Override
    public void clear() {
      backingMap.clear();
    }
  }

  /**
   * {@inheritDoc}
   *

      assertTrue(Thread.holdsLock(mutex));
      return delegate.retainAll(collection);
    }

    @Override
    public void clear() {
      assertTrue(Thread.holdsLock(mutex));
      delegate.clear();
    }

    @Override
    public Object[] toArray() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.toArray();
    }

    @Override

        @Override
        public Iterator<Entry<K, V>> iterator() {
          return delegate().entrySet().iterator();
        }
      };
    }

    @Override
    public void clear() {
      standardClear();
    }

    @Override
    public boolean isEmpty() {
      return standardIsEmpty();
    }
  }

  public static Test suite() {
    TestSuite suite = new TestSuite();

        @Override
        public Iterator<Entry<K, V>> iterator() {
          return delegate().entrySet().iterator();
        }
      };
    }

    @Override
    public void clear() {
      standardClear();
    }

    @Override
    public boolean isEmpty() {
      return standardIsEmpty();
    }
  }

  public static Test suite() {
    TestSuite suite = new TestSuite();

  @Override
  protected abstract Multimap<K, V> delegate();

  @Override
  public Map<K, Collection<V>> asMap() {
    return delegate().asMap();
  }

  @Override
  public void clear() {
    delegate().clear();
  }

  @Override
  public boolean containsEntry(@CheckForNull Object key, @CheckForNull Object value) {
    return delegate().containsEntry(key, value);
  }

  @Override