code: boolean isDirEmpty(INode targetNode) {
  	   boolean dirNotEmpty = true;
      if (!(targetNode != null && targetNode.isDirectory())) {
        return true;
      }
      readLock();
      try {
        assert targetNode != null : "should be taken care in isDir() above";
        if (((INodeDirectory)targetNode).getChildren().size() != 0) {
          dirNotEmpty = false;
        }
      } finally {
        readUnlock();
      }
      return dirNotEmpty;
    }
docs: Return if an inode is empty or not *