code: static boolean isEmptyBlock(Node block) {
      if (!block.isBlock()) {
        return false;
      }
  
      for (Node n = block.getFirstChild(); n != null; n = n.getNext()) {
        if (!n.isEmpty()) {
          return false;
        }
      }
      return true;
    }
docs: Returns whether this a BLOCK node with no children.
  
  @param block The node.