drupal view with text link view causes warning

$this->field_alias is set to "unknown" and the render expects it to be NULL. not sure why / how this is used but it is definitely not set correctly.

causes: Notice: Undefined property: stdClass::$unknown in civicrm_handler_field_link_event->render() in
civicrm/drupal/modules/views/civicrm/civicrm_handler_field_link_event.inc

When I change to return $this->render_link(NULL, $values); there are no complaints but that is just my hack ....