code: def get_empty_ids(self):
          
          cursor = self.get_collection().find(
              {
                  '_id': {'$in': self._document_ids},
                  self._field: {'$exists': True}
              },
              {'_id': True}
          )
  
          return set(self._document_ids) - {doc['_id'] for doc in cursor}
docs: Get documents id with missing targeted field