@Override
  public T pollFirst()
  {
    if (_head == null)
    {
      return null;
    }
    return removeNode(_head);
  }
@Test
  public void testPollFirst()
  {
    List<Integer> control = new ArrayList<>(Arrays.asList(1, 2, 3));
    LinkedDeque<Integer> q = new LinkedDeque<>(control);

    Assert.assertEquals(q.pollFirst(), control.remove(0));
    Assert.assertEquals(q, control);
  }