code: def create_missing(self):
          
          if not hasattr(self, 'name'):
              self.name = gen_alphanumeric().lower()
          super(Domain, self).create_missing()
docs: Customize the process of auto-generating instance attributes.
  
          By default, :meth:`nailgun.entity_fields.StringField.gen_value` can
          produce strings in both lower and upper cases, but domain name should
          be always in lower case due logical reason.