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