@Test
  public void testNull() {
    OrderLinkedRedBlackTree<Integer> tree = new OrderLinkedRedBlackTree<Integer>();
    try {
      tree.insert(null);
      Assert.fail();
    } catch (NullPointerException e) {

    }
    try {
      tree.getPredecessor(null);
      Assert.fail();
    } catch (NullPointerException e) {

    }
    try {
      tree.getSuccessor(null);
      Assert.fail();
    } catch (NullPointerException e) {

    }
    Assert.assertNull(tree.delete(null));
    Assert.assertNull(tree.getNode(null));
    Assert.assertFalse(tree.contains(null));

    tree.insert(0);
    try {
      tree.insert(null);
      Assert.fail();
    } catch (NullPointerException e) {

    }
    try {
      tree.getPredecessor(null);
      Assert.fail();
    } catch (NullPointerException e) {

    }
    try {
      tree.getSuccessor(null);
      Assert.fail();
    } catch (NullPointerException e) {

    }
    Assert.assertNull(tree.delete(null));
    Assert.assertNull(tree.getNode(null));
    Assert.assertFalse(tree.contains(null));
  }