Adding paid payments for orders with state cart throws error

@pietermouton could you provide a bit more details on how to reproduce this issue? I've tried provided steps and can not get an error. Does the order is for an anonymous or authenticated user? What kind of payment are you adding? Maybe yo could provide screenshots of steps or errors?

@tBKoT
The order was placed by an anonymous user, but I think it might also be the issue for an authenticated user.
I've set up my webshop with a custom payment gateway (plugin: manual)

What I do to reproduce:
- Log in as admin
- Go to admin > commerce > order
- Go to carts
- Select a cart
- Go to payments
- Add payment 'custom' (plugin manual)
- Leave the amount as filled in (so the total of the order)
- Check the 'received' checkbox
- Save

I get the error from above.

I've a couple of custom modules active for this project, so there's a chance that it has something to do with these modules (some with eventsubscribers, so one of these can be invoked by the payment being paid).

If you cannot reproduce the error with the steps above, I will look into my custom modules again.

@pietermouton I've checked provided steps and still cannot reproduce the issue. Tried different types of payment, and for the authenticated users too. As you have an error you also should have a bunch of methods/functions from where it goes. You could check there if any of your custom modules triggering there.

Closing it, as still cannot reproduce