docs: def dependency_status(data):
      """Return abstracted status of dependencies.
  
      - ``STATUS_ERROR`` .. one dependency has error status or was deleted
      - ``STATUS_DONE`` .. all dependencies have done status
      - ``None`` .. other
  
      """
      parents_statuses = set(
          DataDependency.objects.filter(
              child=data, kind=DataDependency.KIND_IO
          ).distinct('parent__status').values_list('parent__status', flat=True)
      )
  
      if not parents_statuses:
          return Data.STATUS_DONE
  
      if None in parents_statuses:
          # Some parents have been deleted.
          return Data.STATUS_ERROR
  
      if Data.STATUS_ERROR in parents_statuses:
          return Data.STATUS_ERROR
  
      if len(parents_statuses) == 1 and Data.STATUS_DONE in parents_statuses:
          return Data.STATUS_DONE
  
      return None