}
    };
  }

  /**
   * Deletes and returns the next value from the iterator, or returns {@code null} if there is no
   * such value.
   */
  static <T extends @Nullable Object> @Nullable T pollNext(Iterator<T> iterator) {
    if (iterator.hasNext()) {
      T result = iterator.next();
      iterator.remove();
      return result;
    } else {
      return null;
    }
  }