Program: 46083
Project: 46083
Buggy source:
public void messageReceived(WonderlandClientSender sender,WonderlandClientID clientID,Message message){
  AppContext.getDataManager().markForUpdate(this);
  if (message instanceof ClientConnectMessage) {
    sender.send(clientID,new ClientConnectResponseMessage(presenceInfoList.toArray(new PresenceInfo[0])));
    return;
  }
  if (message instanceof PlayerInRangeListenerMessage) {
    PlayerInRangeListenerMessage msg=(PlayerInRangeListenerMessage)message;
    PresenceInfo info=presenceInfoMap.get(clientID.getID());
    if (info == null) {
      System.out.println("String_Node_Str" + clientID.getID());
      return;
    }
    if (msg.getAdd() == true) {
      PlayerInRangeNotifier notifier=new PlayerInRangeNotifier(info);
      ManagedReference<PlayerInRangeNotifier> notifierRef=AppContext.getDataManager().createReference(notifier);
      notifiers.put(clientID.getID(),notifierRef);
      return;
    }
    ManagedReference<PlayerInRangeNotifier> notifierRef=notifiers.remove(clientID.getID());
    if (notifierRef == null) {
      System.out.println("String_Node_Str" + clientID.getID());
      return;
    }
    notifierRef.get().done();
    return;
  }
  if (message instanceof PresenceInfoAddedMessage) {
    PresenceInfo presenceInfo=((PresenceInfoAddedMessage)message).getPresenceInfo();
    if (presenceInfoList.contains(presenceInfo)) {
      return;
    }
    presenceInfoMap.put(clientID.getID(),presenceInfo);
    presenceInfoList.add(presenceInfo);
    logger.fine("String_Node_Str" + presenceInfo);
    sender.send(message);
    return;
  }
  if (message instanceof PresenceInfoRemovedMessage) {
    PresenceInfo presenceInfo=((PresenceInfoRemovedMessage)message).getPresenceInfo();
    presenceInfoMap.remove(clientID.getID());
    presenceInfoList.remove(presenceInfo);
    sender.send(message);
    return;
  }
  if (message instanceof PresenceInfoChangeMessage) {
    PresenceInfo presenceInfo=((PresenceInfoChangeMessage)message).getPresenceInfo();
    presenceInfoList.remove(presenceInfo);
    presenceInfoList.add(presenceInfo);
    sender.send(message);
    return;
  }
  throw new UnsupportedOperationException("String_Node_Str" + message);
}

Fixed version (ground truth):
public void messageReceived(WonderlandClientSender sender,WonderlandClientID clientID,Message message){
  AppContext.getDataManager().markForUpdate(this);
  if (message instanceof ClientConnectMessage) {
    sender.send(clientID,new ClientConnectResponseMessage(presenceInfoList.toArray(new PresenceInfo[0])));
    return;
  }
  if (message instanceof PlayerInRangeListenerMessage) {
    PlayerInRangeListenerMessage msg=(PlayerInRangeListenerMessage)message;
    PresenceInfo info=presenceInfoMap.get(clientID.getID());
    if (info == null) {
      System.out.println("String_Node_Str" + clientID.getID());
      return;
    }
    if (msg.getAdd() == true) {
      PlayerInRangeNotifier notifier=new PlayerInRangeNotifier(info);
      ManagedReference<PlayerInRangeNotifier> notifierRef=AppContext.getDataManager().createReference(notifier);
      notifiers.put(clientID.getID(),notifierRef);
      return;
    }
    ManagedReference<PlayerInRangeNotifier> notifierRef=notifiers.remove(clientID.getID());
    if (notifierRef == null) {
      System.out.println("String_Node_Str" + clientID.getID());
      return;
    }
    notifierRef.get().done();
    return;
  }
  if (message instanceof PresenceInfoAddedMessage) {
    PresenceInfo presenceInfo=((PresenceInfoAddedMessage)message).getPresenceInfo();
    if (presenceInfoList.contains(presenceInfo)) {
      return;
    }
    if (presenceInfo.clientID != null) {
      presenceInfoMap.put(presenceInfo.clientID,presenceInfo);
    }
    presenceInfoList.add(presenceInfo);
    logger.fine("String_Node_Str" + presenceInfo);
    sender.send(message);
    return;
  }
  if (message instanceof PresenceInfoRemovedMessage) {
    PresenceInfo presenceInfo=((PresenceInfoRemovedMessage)message).getPresenceInfo();
    if (presenceInfo.clientID != null) {
      presenceInfoMap.remove(presenceInfo.clientID);
    }
    presenceInfoList.remove(presenceInfo);
    sender.send(message);
    return;
  }
  if (message instanceof PresenceInfoChangeMessage) {
    PresenceInfo presenceInfo=((PresenceInfoChangeMessage)message).getPresenceInfo();
    presenceInfoList.remove(presenceInfo);
    presenceInfoList.add(presenceInfo);
    sender.send(message);
    return;
  }
  throw new UnsupportedOperationException("String_Node_Str" + message);
}