hasPeeked = false;
      peekedElement = null;
      return result;
    }

    @Override
    public void remove() {
      checkState(!hasPeeked, "Can't remove after you've peeked at next");
      iterator.remove();
    }

    @Override
    @ParametricNullness
    public E peek() {
      if (!hasPeeked) {
        peekedElement = iterator.next();