return this;
    }

    /**
     * Configures this {@code Builder} to order entries by value according to the specified
     * comparator.
     *
     * <p>The sort order is stable, that is, if two entries have values that compare as equivalent,
     * the entry that was inserted first will be first in the built map's iteration order.
     *

  }

  /**
   * An unmodifiable view of a set which may be backed by other sets; this view will change as the
   * backing sets do. Contains methods to copy the data into a new set which will then remain
   * stable. There is usually no reason to retain a reference of type {@code SetView}; typically,
   * you either use it as a plain {@link Set}, or immediately invoke {@link #immutableCopy} or

      }
      return this;
    }

    /**
     * Configures this {@code Builder} to order entries by value according to the specified
     * comparator.
     *
     * <p>The sort order is stable, that is, if two entries have values that compare as equivalent,
     * the entry that was inserted first will be first in the built map's iteration order.
     *

        : ImmutableList.<E>construct(elements.clone());
  }

  /**
   * Returns an immutable list containing the given elements, sorted according to their natural
   * order. The sorting algorithm used is stable, so elements that compare as equal will stay in the
   * order in which they appear in the input.
   *
   * <p>If your data has no duplicates, or you wish to deduplicate elements, use {@code

   *         .build();
   * }</pre>
   *
   * <p>Elements appear in the resulting set in the same order they were first added to the builder.
   *
   * <p>Building does not change the state of the builder, so it is still possible to add more
   * elements and to build again.
   *
   * @since 2.0
   */
  public static class Builder<E> extends ImmutableCollection.ArrayBasedBuilder<E> {

      IdentityHashMap<K, V> newIdentityHashMap() {
    return new IdentityHashMap<>();
  }

  /**
   * Computes the difference between two maps. This difference is an immutable snapshot of the state
   * of the maps at the time this method is called. It will never change, even if the maps change at
   * a later time.
   *
   * <p>Since this method uses {@code HashMap} instances internally, the keys of the supplied maps

      Collector.<@Nullable Object, ToOptionalState, @Nullable Object>of(
          ToOptionalState::new,
          (state, o) -> state.add((o == null) ? NULL_PLACEHOLDER : o),
          ToOptionalState::combine,
          state -> {
            Object result = state.getElement();
            return (result == NULL_PLACEHOLDER) ? null : result;
          },
          Collector.Characteristics.UNORDERED);

  /**

  /**
   * Returns the single element contained in {@code iterator}.
   *
   * @throws NoSuchElementException if the iterator is empty
   * @throws IllegalArgumentException if the iterator contains multiple elements. The state of the
   *     iterator is unspecified.
   */
  @ParametricNullness
  public static <T extends @Nullable Object> T getOnlyElement(Iterator<T> iterator) {
    T first = iterator.next();
    if (!iterator.hasNext()) {