protected function updateRow($rowId, $attributes)
        {
            $cart = $this->getContent();

            $row = $cart->$rowId;

            $row->populate($attributes);

            if(!is_null(array_keys($attributes, array('qty', 'price')))) {
                $row->put('subtotal', $row->qty * $row->price);
            }

            $cart->put($rowId, $row);

            return $cart;
        }