code: final TreeMapEntry<K,V> getLastEntry() {
          TreeMapEntry<K,V> p = root;
          if (p != null)
              while (p.right != null)
                  p = p.right;
          return p;
      }
docs: Returns the last Entry in the TreeMap (according to the TreeMap's
  key-sort function).  Returns null if the TreeMap is empty.