code: private final K getRoundKey(final K key, final boolean upORdown, final boolean acceptEqual) {
  		final TreeEntry<K, V> entry = getRoundEntry(key, upORdown, acceptEqual);
  		if (entry == null) {
  			return null;
  		}
  		return entry.getKey();
  	}
docs: Return ceilingKey, floorKey, higherKey or lowerKey
  
  @param key the key
  @param upORdown true returns ceilingKey, false floorKey
  @param acceptEqual true returns equal keys, otherwise, only higher or lower
  @return the key found or null if not found