public ActionResult AddFavouriteTopic(int topicID)
{
string me = whoami();
Topic topic = _topicManager.FindTopic(topicID);
if (topic == null)
{
throw new TopicNotFoundException();
}
MembershipHelper.CheckMembership(topic.GroupID, me);
_topicManager.AddFavouriteTopic(whoami(), topicID);
return(new ActionResult());
}