An empty Workers process can be started

process = cli.request('CreateElementsWorkflow', body={'corpus': CORPUS_ID})
cli.request('StartProcess', id=process['id'], body={})

This creates and starts a completely useless workers process with nothing other than the initialisation task.

https://preprod.arkindex.teklia.com/process/8056b43f-849d-4707-affb-ffc5afcd6496/0

This should not be possible; StartProcess should check whether there are any worker runs, or whether the thumbnails option was set to true, before starting.