Maintenance error has no error code, causing crash

[alimony]

This is from Sentry:

Seems like at least this error payload has no error code, causing a crash. I don't know if Fortnox has changed something on a more general level, might be good to look into.

[xalien10]

@alimony I'll take a look if there is anything changed in fortnox that causing this error to occur