code: public RedBlackTreeNode<Key, Value> floorNode(Key key) {
  	if (isEmpty()) {
  	    return null;
  	}
  	RedBlackTreeNode<Key, Value> x = floor(root, key);
  	if (x == null) {
  	    return null;
  	} else {
  	    return x;
  	}
      }
docs: Returns the largest node with key in the symbol table less than or equal to
  <code>key</code>.
  
  @param key
  the key
  @return the largest key in the symbol table less than or equal to
  <code>key</code>
  @throws NoSuchElementException
  if there is no such key