Program: 159154
Project: 159154
Buggy source:
public synchronized boolean joinTable(UUID userId,String name,String playerType,int skill,DeckCardLists deckList) throws MageException {
  User user=UserManager.getInstance().getUser(userId);
  if (user == null) {
    return false;
  }
  if (table.getState() != TableState.WAITING) {
    user.showUserMessage("String_Node_Str","String_Node_Str");
    return false;
  }
  Seat seat=table.getNextAvailableSeat(playerType);
  if (seat == null) {
    user.showUserMessage("String_Node_Str","String_Node_Str");
    return false;
  }
  Deck deck=Deck.load(deckList,false,false);
  if (!Main.isTestMode() && !table.getValidator().validate(deck)) {
    StringBuilder sb=new StringBuilder("String_Node_Str").append(name).append("String_Node_Str").append(table.getValidator().getName()).append("String_Node_Str");
    for (    Map.Entry<String,String> entry : table.getValidator().getInvalid().entrySet()) {
      sb.append(entry.getKey()).append("String_Node_Str").append(entry.getValue()).append("String_Node_Str");
    }
    sb.append("String_Node_Str");
    user.showUserMessage("String_Node_Str",sb.toString());
    return false;
  }
  Player player=createPlayer(name,seat.getPlayerType(),skill);
  if (player == null) {
    String message=new StringBuilder("String_Node_Str").append(name).append("String_Node_Str").append(seat.getPlayerType().toString()).toString();
    logger.warn(new StringBuilder("String_Node_Str").append(user.getName()).append("String_Node_Str").append(message).toString());
    user.showUserMessage("String_Node_Str",message);
    return false;
  }
  if (!player.canJoinTable(table)) {
    user.showUserMessage("String_Node_Str",new StringBuilder("String_Node_Str").append(seat.getPlayerType()).append("String_Node_Str").toString());
    return false;
  }
  match.addPlayer(player,deck);
  table.joinTable(player,seat);
  logger.trace(player.getName() + "String_Node_Str" + table.getId());
  if (seat.getPlayer().isHuman()) {
    user.addTable(player.getId(),table);
    user.joinedTable(table.getRoomId(),table.getId(),false);
    userPlayerMap.put(userId,player.getId());
  }
  return true;
}

Fixed version (ground truth):
public synchronized boolean joinTable(UUID userId,String name,String playerType,int skill,DeckCardLists deckList) throws MageException {
  User user=UserManager.getInstance().getUser(userId);
  if (user == null) {
    return false;
  }
  if (table.getState() != TableState.WAITING) {
    user.showUserMessage("String_Node_Str","String_Node_Str");
    return false;
  }
  Seat seat=table.getNextAvailableSeat(playerType);
  if (seat == null) {
    user.showUserMessage("String_Node_Str","String_Node_Str");
    return false;
  }
  Deck deck=Deck.load(deckList,false,false);
  if (!Main.isTestMode() && !table.getValidator().validate(deck)) {
    StringBuilder sb=new StringBuilder("String_Node_Str").append(name).append("String_Node_Str").append(table.getValidator().getName()).append("String_Node_Str");
    for (    Map.Entry<String,String> entry : table.getValidator().getInvalid().entrySet()) {
      sb.append(entry.getKey()).append("String_Node_Str").append(entry.getValue()).append("String_Node_Str");
    }
    sb.append("String_Node_Str");
    user.showUserMessage("String_Node_Str",sb.toString());
    if (isOwner(userId)) {
      logger.debug("String_Node_Str" + table.getId());
      TableManager.getInstance().removeTable(table.getId());
    }
    return false;
  }
  Player player=createPlayer(name,seat.getPlayerType(),skill);
  if (player == null) {
    String message=new StringBuilder("String_Node_Str").append(name).append("String_Node_Str").append(seat.getPlayerType().toString()).toString();
    logger.warn(new StringBuilder("String_Node_Str").append(user.getName()).append("String_Node_Str").append(message).toString());
    user.showUserMessage("String_Node_Str",message);
    return false;
  }
  if (!player.canJoinTable(table)) {
    user.showUserMessage("String_Node_Str",new StringBuilder("String_Node_Str").append(seat.getPlayerType()).append("String_Node_Str").toString());
    return false;
  }
  match.addPlayer(player,deck);
  table.joinTable(player,seat);
  logger.trace(player.getName() + "String_Node_Str" + table.getId());
  if (seat.getPlayer().isHuman()) {
    user.addTable(player.getId(),table);
    user.joinedTable(table.getRoomId(),table.getId(),false);
    userPlayerMap.put(userId,player.getId());
  }
  return true;
}