checkNotNull(collection);
    return (collection instanceof EnumSet)
        ? EnumSet.complementOf((EnumSet<E>) collection)
        : makeComplementByHand(collection, type);
  }

  @J2ktIncompatible
  @GwtIncompatible
  private static <E extends Enum<E>> EnumSet<E> makeComplementByHand(
      Collection<E> collection, Class<E> type) {
    EnumSet<E> result = EnumSet.allOf(type);

    @Override
    public Entry<K, Collection<V>>[] createArray(int length) {
      return (Entry<K, Collection<V>>[]) new Entry<?, ?>[length];
    }

    @Override
    public Iterable<Entry<K, Collection<V>>> order(List<Entry<K, Collection<V>>> insertionOrder) {
      Map<K, Collection<V>> map = new HashMap<>();
      List<Entry<K, V>> builder = new ArrayList<>();
      for (Entry<K, Collection<V>> entry : insertionOrder) {

   * elements than the collection), the element in the array immediately following the end of the
   * collection is set to {@code null}. This is useful in determining the length of the collection
   * <i>only</i> if the caller knows that the collection does not contain any null elements.
   *
   * <p>This method returns the elements in the order they are returned by the collection's
   * iterator.
   *

      K key = entry.getKey();
      V value = entry.getValue();
      Collection<V> collection = multimap().get(key);
      assertNotNull(collection);
      Collection<V> expectedCollection = Helpers.copyToList(collection);

      multimap().remove(key, value);
      expectedCollection.remove(value);

      assertEqualIgnoringOrder(expectedCollection, collection);

  }

  @Override
  Collection<V> wrapCollection(@ParametricNullness K key, Collection<V> collection) {
    return wrapList(key, (List<V>) collection, null);
  }

  // Following Javadoc copied from ListMultimap.

  /**
   * {@inheritDoc}
   *
   * <p>Because the values for a given key may have duplicates and follow the insertion ordering,
   * this method returns a {@link List}, instead of the {@link Collection} specified in the {@link

  }

  @Override
  Collection<V> wrapCollection(@ParametricNullness K key, Collection<V> collection) {
    return wrapList(key, (List<V>) collection, null);
  }

  // Following Javadoc copied from ListMultimap.

  /**
   * {@inheritDoc}
   *
   * <p>Because the values for a given key may have duplicates and follow the insertion ordering,
   * this method returns a {@link List}, instead of the {@link Collection} specified in the {@link

            }
        }
    }

    @Override
    public Collection<? extends Metadata> prepare(Collection<? extends Artifact> artifacts) {
        return Collections.emptyList();
    }

    @Override
    public Artifact transformArtifact(Artifact artifact) {
        return artifact;
    }

    @Override
    public Collection<? extends Metadata> finish(Collection<? extends Artifact> artifacts) {

 * collection instance can only be one size at once.
 *
 * @author George van den Driessche
 */
@SuppressWarnings("rawtypes") // maybe avoidable if we rework the whole package?
@GwtCompatible
public enum CollectionSize implements Feature<Collection>, Comparable<CollectionSize> {
  /** Test an empty collection. */
  ZERO(0),
  /** Test a one-element collection. */
  ONE(1),
  /** Test a three-element collection. */
  SEVERAL(3),

    resetContainer(
        Helpers.mapEntry(k0(), v0()), Helpers.mapEntry(k1(), v0()), Helpers.mapEntry(k0(), v3()));
    Set<Entry<K, Collection<V>>> expected = Sets.newHashSet();
    expected.add(Helpers.mapEntry(k0(), (Collection<V>) Sets.newHashSet(v0(), v3())));
    expected.add(Helpers.mapEntry(k1(), (Collection<V>) Sets.newHashSet(v0())));
    new EqualsTester().addEqualityGroup(expected, multimap().asMap().entrySet()).testEquals();
  }

    resetContainer(
        Helpers.mapEntry(k0(), v0()), Helpers.mapEntry(k1(), v0()), Helpers.mapEntry(k0(), v3()));
    Set<Entry<K, Collection<V>>> expected = Sets.newHashSet();
    expected.add(Helpers.mapEntry(k0(), (Collection<V>) Lists.newArrayList(v0(), v3())));
    expected.add(Helpers.mapEntry(k1(), (Collection<V>) Lists.newArrayList(v0())));
    new EqualsTester().addEqualityGroup(expected, multimap().asMap().entrySet()).testEquals();
  }