new_contents: # -*- coding: utf-8; -*-
  # This file is part of Superdesk.
  # For the full copyright and license information, please see the
  # AUTHORS and LICENSE files distributed with this source code, or
  # at https://www.sourcefabric.org/superdesk/license
  #
  # Author  : petr
  # Creation: 2020-11-18 16:06
  
  from superdesk.commands.data_updates import DataUpdate
  
  
  class DataUpdate(DataUpdate):
  
      resource = 'sequences'
  
      def forwards(self, mongodb_collection, mongodb_database):
          return mongodb_collection.delete_many({'key': None})
  
      def backwards(self, mongodb_collection, mongodb_database):
          pass
  
subject: add migration to remove sequences with null key (#2050)