protected function getSaleItemFromEvent(ResourceEventInterface $event)
    {
        $item = $event->getResource();

        if (!$item instanceof OrderItemInterface) {
            throw new InvalidArgumentException("Expected instance of OrderItemInterface");
        }

        return $item;
    }
protected function getSaleItemFromEvent(ResourceEventInterface $event)
    {
        $item = $event->getResource();

        if (!$item instanceof OrderItemInterface) {
            throw new InvalidArgumentException("Expected instance of OrderItemInterface");
        }

        return $item;
    }
@inheritdoc

@return OrderItemInterface