code: final TreeMapEntry<K,V> getEntryUsingComparator(Object key) {
          @SuppressWarnings("unchecked")
              K k = (K) key;
          Comparator<? super K> cpr = comparator;
          if (cpr != null) {
              TreeMapEntry<K,V> p = root;
              while (p != null) {
                  int cmp = cpr.compare(k, p.key);
                  if (cmp < 0)
                      p = p.left;
                  else if (cmp > 0)
                      p = p.right;
                  else
                      return p;
              }
          }
          return null;
      }
docs: Version of getEntry using comparator. Split off from getEntry
  for performance. (This is not worth doing for most methods,
  that are less dependent on comparator performance, but is
  worthwhile here.)