}

  /**
   * Returns an iterator containing only {@code value}.
   *
   * <p>The {@link Iterable} equivalent of this method is {@link Collections#singleton}.
   */
  public static <T extends @Nullable Object> UnmodifiableIterator<T> singletonIterator(
      @ParametricNullness T value) {
    if (value != null) {
      return new SingletonIterator<>(value);
    }