Undefined property: CI_DB_mysqli_driver::$ar_orderby?

I have a CodeIgniter (version 3)
Message: Undefined property: CI_DB_mysqli_driver::$ar_orderby

Filename: core/MY_Model.php

Line Number: 38

Backtrace:

File: /var/www/html/public/application/core/MY_Model.php
Line: 38
Function: _error_handler

Line Number: 38 and here you are

if (!count($this->db->ar_orderby)) {
$this->db->order_by($this->_order_by);
}
return $this->db->get($this->_table_name)->$method();