Cart/Entity/CartItem.php
protected function assertItemClass(Common\SaleItemInterface $child)
    {
        if (!$child instanceof Model\CartItemInterface) {
            throw new InvalidArgumentException("Expected instance of " . Model\CartItemInterface::class);
        }
    }
protected function assertItemClass(Common\SaleItemInterface $child)
    {
        if (!$child instanceof Model\CartItemInterface) {
            throw new InvalidArgumentException("Expected instance of " . Model\CartItemInterface::class);
        }
    }
Asserts that the given sale item is an instance of the expected class.

@param Common\SaleItemInterface $child