docs: @Override
  	public void start(LeaderContender contender) throws Exception {
  		checkNotNull(contender, "contender");
  
  		synchronized (lock) {
  			checkState(!shutdown, "service is shut down");
  			checkState(proposedLeader == null, "service already started");
  
  			// directly grant leadership to the given contender
  			proposedLeader = contender;
  			notificationExecutor.execute(new GrantLeadershipCall(contender, leaderId));
  		}
  	}