@GwtIncompatible // works but takes 5 minutes to run
  public void testPeekingIteratorAcceptsNullElements() {
    actsLikeIteratorHelper(Lists.<@Nullable String>newArrayList(null, "A", null));
  }

  public void testPeekOnEmptyList() {
    List<?> list = emptyList();
    Iterator<?> iterator = list.iterator();
    PeekingIterator<?> peekingIterator = peekingIterator(iterator);