Bug - third party sponsor is not mandatory field

On e3.20.1:

  • go to org / third party
  • add an item, leave sponsor empty
  • you can save the item

this could present serious problems for visualisations as items do not have an owner

ref: https://github.com/eramba/eramba/issues/4390
ref: https://eramba.zendesk.com/agent/tickets/21616