Program: 32573
Project: 32573
Buggy source:
@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.generalHasNoGuild);
    return;
  }
  if (!user.isOwner()) {
    player.sendMessage(messages.generalIsNotOwner);
    return;
  }
  Guild guild=user.getGuild();
  if (guild.getAllies() == null || guild.getAllies().isEmpty()) {
    player.sendMessage(messages.breakHasNotAllies);
    return;
  }
  if (args.length < 1) {
    List<String> list=messages.breakAlliesList;
    String iss=StringUtils.toString(GuildUtils.getNames(guild.getAllies()),true);
    for (    String msg : list) {
      player.sendMessage(msg.replace("String_Node_Str",iss));
    }
    return;
  }
  String tag=args[0];
  Guild oppositeGuild=GuildUtils.byTag(tag);
  if (oppositeGuild == null) {
    player.sendMessage(messages.generalGuildNotExists.replace("String_Node_Str",tag));
    return;
  }
  if (!guild.getAllies().contains(oppositeGuild)) {
    player.sendMessage(messages.breakAllyExists.replace("String_Node_Str",oppositeGuild.getName()).replace("String_Node_Str",tag));
  }
  if (!SimpleEventHandler.handle(new GuildBreakAllyEvent(EventCause.USER,user,guild,oppositeGuild))) {
    return;
  }
  guild.removeAlly(oppositeGuild);
  oppositeGuild.removeAlly(guild);
  for (  User u : guild.getMembers()) {
    IndependentThread.action(ActionType.PREFIX_UPDATE_GUILD,u,oppositeGuild);
  }
  for (  User u : oppositeGuild.getMembers()) {
    IndependentThread.action(ActionType.PREFIX_UPDATE_GUILD,u,guild);
  }
  Player owner=oppositeGuild.getOwner().getPlayer();
  if (owner != null) {
    owner.sendMessage(messages.allyIDone.replace("String_Node_Str",guild.getName()).replace("String_Node_Str",guild.getTag()));
  }
  player.sendMessage(messages.breakDone.replace("String_Node_Str",oppositeGuild.getName()).replace("String_Node_Str",oppositeGuild.getTag()));
}

Fixed version (ground truth):
@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.generalHasNoGuild);
    return;
  }
  if (!user.isOwner()) {
    player.sendMessage(messages.generalIsNotOwner);
    return;
  }
  Guild guild=user.getGuild();
  if (guild.getAllies() == null || guild.getAllies().isEmpty()) {
    player.sendMessage(messages.breakHasNotAllies);
    return;
  }
  if (args.length < 1) {
    List<String> list=messages.breakAlliesList;
    String iss=StringUtils.toString(GuildUtils.getNames(guild.getAllies()),true);
    for (    String msg : list) {
      player.sendMessage(msg.replace("String_Node_Str",iss));
    }
    return;
  }
  String tag=args[0];
  Guild oppositeGuild=GuildUtils.getByTag(tag);
  if (oppositeGuild == null) {
    player.sendMessage(messages.generalGuildNotExists.replace("String_Node_Str",tag));
    return;
  }
  if (!guild.getAllies().contains(oppositeGuild)) {
    player.sendMessage(messages.breakAllyExists.replace("String_Node_Str",oppositeGuild.getName()).replace("String_Node_Str",tag));
  }
  if (!SimpleEventHandler.handle(new GuildBreakAllyEvent(EventCause.USER,user,guild,oppositeGuild))) {
    return;
  }
  guild.removeAlly(oppositeGuild);
  oppositeGuild.removeAlly(guild);
  for (  User u : guild.getMembers()) {
    IndependentThread.action(ActionType.PREFIX_UPDATE_GUILD,u,oppositeGuild);
  }
  for (  User u : oppositeGuild.getMembers()) {
    IndependentThread.action(ActionType.PREFIX_UPDATE_GUILD,u,guild);
  }
  Player owner=oppositeGuild.getOwner().getPlayer();
  if (owner != null) {
    owner.sendMessage(messages.allyIDone.replace("String_Node_Str",guild.getName()).replace("String_Node_Str",guild.getTag()));
  }
  player.sendMessage(messages.breakDone.replace("String_Node_Str",oppositeGuild.getName()).replace("String_Node_Str",oppositeGuild.getTag()));
}