Codeigniter 4 Model set() returns error

Input: Entity Object 
Error returned: "Illegal offset type" on line 685 in \codeigniter4\framework\system\Model.php.

Example:

PHP Code:

        if ((new EquipmentModel)->where('order_id', $order_id)->first()) {
            (new EquipmentModel)->where('order_id', $order_id)->set($equipment)->update();
        } else {
            $equipmentModel->insert($equipment);
        }