*
 * @author Louis Wasserman
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
class FilteredKeyMultimap<K extends @Nullable Object, V extends @Nullable Object>
    extends AbstractMultimap<K, V> implements FilteredMultimap<K, V> {
  final Multimap<K, V> unfiltered;
  final Predicate<? super K> keyPredicate;

  FilteredKeyMultimap(Multimap<K, V> unfiltered, Predicate<? super K> keyPredicate) {
    this.unfiltered = checkNotNull(unfiltered);