Error gets thrown, if commerce product variation doesn't have a price set.

This fixes the error thrown. But I am not 100% sure, if "NULL" is a good fallback here.

Thanks @Grevil yes I think it might be fine. Another alternative would be to not add that product at all, but that might also be undeserved in some cases. So let's do it like this for now.

Automatically closed - issue fixed for 2 weeks with no activity.