[Koha] Delete patron via REST API - Missing property - Status 500

[zefanja]

Hello,

I want to delete patrons with the REST API. If the patron has no 
checkouts, everything works fine. But when the patron has checkouts, I 
get this as response from my HTTP DELETE request:

{"errors":[{"message":"Missing property.","path":"\/errors"}],"status":500}

The API docs say that it should return a 409 status with errors → 
has_checkouts

https://api.koha-community.org/#operation/deletePatron

Any ideas? I send the requests to this url: 
https://our-library-intra.com/api/v1/patrons/23

Regards,
Stephan