#vulnerable code 
                                @Override
    public void execute(CommandSender sender, String[] args) {
        MessagesConfig m = Messages.getInstance();
        User user = User.get((Player) sender);

        if (user.isSpy()) {
            user.setSpy(false);
            sender.sendMessage(m.adminStopSpy);
        } else {
            user.setSpy(true);
            sender.sendMessage(m.adminStartSpy);
        }
    } 
                            #location 11 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public void execute(CommandSender sender, String[] args) {
        MessagesConfig messages = Messages.getInstance();
        User user = User.get((Player) sender);

        if (user.isSpy()) {
            user.setSpy(false);
            sender.sendMessage(messages.adminStopSpy);
        } else {
            user.setSpy(true);
            sender.sendMessage(messages.adminStartSpy);
        }
    }