.collect(Collectors.toList());
            try {
                List<Future<InterimResult>> futures = executor.invokeAll(tasks);
                List<InterimResult> list = new ArrayList<>();
                for (Future<InterimResult> future : futures) {
                    InterimResult interimResult = future.get();
                    list.add(interimResult);
                }
                return list;

   * asList}{@code (...))}, or for creating an empty set then calling {@link Collections#addAll}.
   * This method is not actually very useful and will likely be deprecated in the future.
   */
  @SuppressWarnings("nullness") // TODO: b/316358623 - Remove after checker fix.
  public static <E extends @Nullable Object> HashSet<E> newHashSet(E... elements) {

   * values are merged using the specified merging function. If the merging function returns {@code
   * null}, then the collector removes the value that has been computed for the key thus far (though
   * future occurrences of the key would reinsert it).
   *
   * <p>Entries will appear in the encounter order of the first occurrence of the key.
   *
   * @since 33.2.0 (available since 21.0 in guava-jre)
   */

     * assume that this field is non-null.
     */
    @CheckForNull ObjectCountHashMap<E> contents;

    /**
     * If build() has been called on the current contents multiset, we need to copy it on any future
     * modifications, or we'll modify the already-built ImmutableMultiset.
     */
    boolean buildInvoked = false;
    /**

                  ImmutableList.<K>asImmutableList(sortedKeys), comparator),
              ImmutableList.<V>asImmutableList(sortedValues));
      }
    }

    /**
     * Throws UnsupportedOperationException. A future version may support this operation. Then the
     * value for any given key will be the one that was last supplied in a {@code put} operation for
     * that key.
     *
     * @throws UnsupportedOperationException always

@IgnoreJRERequirement // Users will use this only if they're already using streams.
@Beta // TODO: b/288085449 - Remove.
public final class MoreCollectors {

  /*
   * TODO(lowasser): figure out if we can convert this to a concurrent AtomicReference-based
   * collector without breaking j2cl?
   */
  private static final Collector<Object, ?, Optional<Object>> TO_OPTIONAL =
      Collector.of(

    return (UnmodifiableListIterator<T>) ArrayItr.EMPTY;
  }

  /**
   * This is an enum singleton rather than an anonymous class so ProGuard can figure out it's only
   * referenced by emptyModifiableIterator().
   */
  private enum EmptyModifiableIterator implements Iterator<Object> {
    INSTANCE;

    @Override
    public boolean hasNext() {

    assertEquals("b", consumingIterator.next());
    assertThat(list).isEmpty();

    assertFalse(consumingIterator.hasNext());
  }

  @GwtIncompatible // ?
  // TODO: Figure out why this is failing in GWT.
  public void testConsumingIterator_duelingIterators() {
    // Test data
    List<String> list = Lists.newArrayList("a", "b");

    // Test & Verify