message: fix missing datasource error message
diff: @@ -1229,7 +1229,10 @@ class Superset(BaseSupersetView):
  datasource = form_data.get('datasource', '')
  if '__' in datasource:
  datasource_id, datasource_type = datasource.split('__')
  - datasource_id = int(datasource_id)
  + # The case where the datasource has been deleted
  + datasource_id = None if datasource_id == 'None' else datasource_id
  +
  + datasource_id = int(datasource_id) if datasource_id else None
  return datasource_id, datasource_type
  @log_this
  