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

        if (user.hasGuild()) {
            p.sendMessage(m.joinHasGuild);
            return;
        }

        List<InvitationList.Invitation> invitations = InvitationList.getInvitationsFor(p);
        if (invitations.size() == 0) {
            p.sendMessage(m.joinHasNotInvitation);
            return;
        }

        if (args.length < 1) {
            String guildNames = StringUtils.toString(InvitationList.getInvitationGuildNames(p), false);
            for (String msg : m.joinInvitationList) {
                p.sendMessage(msg.replace("{GUILDS}", guildNames));
            }
            
            return;
        }

        String tag = args[0];
        if (!GuildUtils.tagExists(tag)) {
            p.sendMessage(m.joinTagExists);
            return;
        }

        if (!InvitationList.hasInvitationFrom(p, GuildUtils.byTag(tag))) {
            p.sendMessage(m.joinHasNotInvitationTo);
            return;
        }

        List<ItemStack> itemsList = Settings.getConfig().joinItems;
        for (ItemStack itemStack : itemsList) {
            if (!p.getInventory().containsAtLeast(itemStack, itemStack.getAmount())) {
                String msg = m.joinItems;
                if (msg.contains("{ITEM}")) {
                    StringBuilder sb = new StringBuilder();
                    sb.append(itemStack.getAmount());
                    sb.append(" ");
                    sb.append(itemStack.getType().toString().toLowerCase());
                    msg = msg.replace("{ITEM}", sb.toString());
                }
                
                if (msg.contains("{ITEMS}")) {
                    ArrayList<String> list = new ArrayList<String>();
                    for (ItemStack it : itemsList) {
                        StringBuilder sb = new StringBuilder();
                        sb.append(it.getAmount());
                        sb.append(" ");
                        sb.append(it.getType().toString().toLowerCase());
                        list.add(sb.toString());
                    }
                    
                    msg = msg.replace("{ITEMS}", StringUtils.toString(list, true));
                }
                
                p.sendMessage(msg);
                return;
            }
            
            p.getInventory().removeItem(itemStack);
        }

        Guild guild = GuildUtils.byTag(tag);

        InvitationList.expireInvitation(guild, p);

        guild.addMember(user);
        user.setGuild(guild);

        IndependentThread.action(ActionType.PREFIX_GLOBAL_ADD_PLAYER, user.getOfflineUser());
        p.sendMessage(m.joinToMember.replace("{GUILD}", guild.getName()).replace("{TAG}", guild.getTag()));

        Player owner = guild.getOwner().getPlayer();
        if (owner != null) {
            owner.sendMessage(m.joinToOwner.replace("{PLAYER}", p.getName()));
        }

        Bukkit.broadcastMessage(m.broadcastJoin.replace("{PLAYER}", p.getName()).replace("{GUILD}", guild.getName()).replace("{TAG}", tag));
    } 
                            #location 74 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public void execute(CommandSender sender, String[] args) {
        MessagesConfig messages = Messages.getInstance();
        Player player = (Player) sender;
        User user = User.get(player);

        if (user.hasGuild()) {
            player.sendMessage(messages.joinHasGuild);
            return;
        }

        List<InvitationList.Invitation> invitations = InvitationList.getInvitationsFor(player);

        if (invitations.size() == 0) {
            player.sendMessage(messages.joinHasNotInvitation);
            return;
        }

        if (args.length < 1) {
            String guildNames = StringUtils.toString(InvitationList.getInvitationGuildNames(player), false);
            for (String msg : messages.joinInvitationList) {
                player.sendMessage(msg.replace("{GUILDS}", guildNames));
            }
            
            return;
        }

        String tag = args[0];
        Guild guild = Guild.get(tag);

        if (guild == null) {
            player.sendMessage(messages.joinTagExists);
            return;
        }

        if (!InvitationList.hasInvitationFrom(player, GuildUtils.byTag(tag))) {
            player.sendMessage(messages.joinHasNotInvitationTo);
            return;
        }

        List<ItemStack> itemsList = Settings.getConfig().joinItems;

        for (ItemStack itemStack : itemsList) {
            if (!player.getInventory().containsAtLeast(itemStack, itemStack.getAmount())) {
                String msg = messages.joinItems;
                if (msg.contains("{ITEM}")) {
                    StringBuilder sb = new StringBuilder();
                    sb.append(itemStack.getAmount());
                    sb.append(" ");
                    sb.append(itemStack.getType().toString().toLowerCase());
                    msg = msg.replace("{ITEM}", sb.toString());
                }
                
                if (msg.contains("{ITEMS}")) {
                    ArrayList<String> list = new ArrayList<String>();
                    for (ItemStack it : itemsList) {
                        StringBuilder sb = new StringBuilder();
                        sb.append(it.getAmount());
                        sb.append(" ");
                        sb.append(it.getType().toString().toLowerCase());
                        list.add(sb.toString());
                    }
                    
                    msg = msg.replace("{ITEMS}", StringUtils.toString(list, true));
                }
                
                player.sendMessage(msg);
                return;
            }
            
            player.getInventory().removeItem(itemStack);
        }

        InvitationList.expireInvitation(guild, player);
        guild.addMember(user);
        user.setGuild(guild);
        IndependentThread.action(ActionType.PREFIX_GLOBAL_ADD_PLAYER, user.getOfflineUser());

        MessageTranslator translator = new MessageTranslator()
                .register("{GUILD}", guild.getName())
                .register("{TAG}", guild.getTag())
                .register("{PLAYER}", player.getName());

        player.sendMessage(translator.translate(messages.joinToMember));
        Bukkit.broadcastMessage(translator.translate(messages.broadcastJoin));

        Player owner = guild.getOwner().getPlayer();
        if (owner != null) {
            owner.sendMessage(translator.translate(messages.joinToOwner));
        }
    }