if (size() < result.length) {
              // It works around a GWT bug where elements after last is not
              // properly null'ed.
              @Nullable Object[] unsoundlyCovariantArray = result;
              unsoundlyCovariantArray[size()] = null;
            }
            return result;
          }
        });
  }

  @Override
  ImmutableSet<K> createKeySet() {