`/api/:category/:id/history` returns status code 500

e.g.

curl https://sshoc-marketplace-api.acdh-dev.oeaw.ac.at/api/tools-services/3IAyEp/history

returns

{"timestamp":"2021-07-23 09:04:40","status":500,"error":"Cannot instantiate abstract class or interface:  : eu.sshopencloud.marketplace.model.items.DigitalObject; nested exception is org.hibernate.InstantiationException: Cannot instantiate abstract class or interface:  : eu.sshopencloud.marketplace.model.items.DigitalObject"}