code: def add_event_type(self, name):
          
          if name in self.event_types:
              lg.info('Event type ' + name + ' exists already.')
              return
  
          events = self.rater.find('events')
          new_event_type = SubElement(events, 'event_type')
          new_event_type.set('type', name)
          self.save()
docs: Raises
          ------
          IndexError
              When there is no selected rater