@Override
  public T pollLast()
  {
    if (_tail == null)
    {
      return null;
    }
    return removeNode(_tail);
  }
@Test
  public void testEmptyPollLast()
  {
    LinkedDeque<Object> q = new LinkedDeque<>();
    Assert.assertNull(q.pollLast(), "pollLast on empty queue should return null");
  }