Response not specified when updating non-existing service instance

[gosua]

What is the problem?
My problem is that I don't find in the specification what the service broker shall return in case an udpate of a non-existing service instance was initiated: https://github.com/openservicebrokerapi/servicebroker/blob/master/spec.md#updating-a-service-instance.

Example: PATCH /v2/service_instances/fake-id-which-does-not-exist

Additional context
Interesting is that the specification prescribes the reponse in case a deprovisioning of a non-existing service instance was initiated: https://github.com/openservicebrokerapi/servicebroker/blob/master/spec.md#response-10

410 Gone | MUST be returned if the Service Instance does not exist.

What is my question?
Which HTTP code shall be returned when trying to update non-existing service instance?