Comment 7 for bug 1746509

I've reproduced this behavior in a functional test: https://review.openstack.org/555058

The problem occurs during an instance list across cells (no scatter-gather) when joining with a nova-compute service record with no uuid. In the API, we use 'services' as a column to join in order to do the instance 'show':

https://github.com/openstack/nova/blob/9465d1c/nova/api/openstack/compute/servers.py#L298

and when we go to query for instances from cell databases, we hit this error.