The current model expects the jobs, shipments to have all or none the field skills
Moreover, having a field with an empty array returns an error Missing skills.
It is expected to provide at least a dummy 'skill' for every jobs and vehicles.

My expectation was, that a vehicle with an empty array of skills could serve jobs or shipments without particular need (with an empty array of skills as well). And a job with an empty set of skills can be served by any vehicle.