public void addFirst(PDOutlineItem newChild)
    {
        requireSingleNode(newChild);
        prepend(newChild);
        updateParentOpenCountForAddedChild(newChild);
    }
@Test
    void cannotAddFirstAList()
    {
        PDOutlineItem child = new PDOutlineItem();
        child.insertSiblingAfter(new PDOutlineItem());
        child.insertSiblingAfter(new PDOutlineItem());
        assertThrows(IllegalArgumentException.class, () -> root.addFirst(child));
    }