Cancels an event in Exchange.  ::

        event = service.calendar().get_event(id='KEY HERE')
        event.cancel()

    This will send notifications to anyone who has not declined the meeting.

def cancel(self):
    """
    Cancels an event in Exchange.  ::

        event = service.calendar().get_event(id='KEY HERE')
        event.cancel()

    This will send notifications to anyone who has not declined the meeting.
    """
    if not self.id:
      raise TypeError(u"You can't delete an event that hasn't been created yet.")

    self.refresh_change_key()
    self.service.send(soap_request.delete_event(self))
    # TODO rsanders high - check return status to make sure it was actually sent
    return None