guard against missing shipping invoice

backend/src/modules/order/services/OrderService.ts

@@ -250,6 +250,10 @@ export class OrderService {
             amountFiat: deliveryCost
         });
 
+        if (!shippingInvoice) {
+            throw new InternalServerErrorException('Failed to issue shipping invoice');
+        }
+
         await this.orderRepo.update(orderId, {
             shippingInvoice: { id: shippingInvoice.id },
             quotedAt