Program: 58047
Project: 58047
Buggy source:
@Override public boolean execute(final PlotPlayer plr,final String... args){
  if (args.length < 2) {
    MainUtil.sendMessage(plr,C.HELPER_NEED_ARGUMENT);
    return true;
  }
  final Location loc=plr.getLocation();
  final Plot plot=MainUtil.getPlot(loc);
  if (plot == null) {
    return !sendMessage(plr,C.NOT_IN_PLOT);
  }
  if ((plot == null) || !plot.hasOwner()) {
    MainUtil.sendMessage(plr,C.PLOT_UNOWNED);
    return false;
  }
  if (!plot.getOwner().equals(UUIDHandler.getUUID(plr)) && !Permissions.hasPermission(plr,"String_Node_Str")) {
    MainUtil.sendMessage(plr,C.NO_PLOT_PERMS);
    return true;
  }
  if (args[0].equalsIgnoreCase("String_Node_Str")) {
    UUID uuid;
    if (args[1].equalsIgnoreCase("String_Node_Str")) {
      uuid=DBFunc.everyone;
    }
 else {
      uuid=UUIDHandler.getUUID(args[1]);
    }
    if (uuid == null) {
      MainUtil.sendMessage(plr,C.INVALID_PLAYER,args[1]);
      return false;
    }
    if (!plot.helpers.contains(uuid)) {
      if (plot.owner.equals(uuid)) {
        MainUtil.sendMessage(plr,C.ALREADY_OWNER);
        return false;
      }
      if (plot.trusted.contains(uuid)) {
        plot.trusted.remove(uuid);
        DBFunc.removeTrusted(loc.getWorld(),plot,uuid);
      }
      if (plot.denied.contains(uuid)) {
        plot.denied.remove(uuid);
        DBFunc.removeDenied(loc.getWorld(),plot,uuid);
      }
      plot.addHelper(uuid);
      DBFunc.setHelper(loc.getWorld(),plot,uuid);
      EventUtil.manager.callHelper(plr,plot,uuid,true);
    }
 else {
      MainUtil.sendMessage(plr,C.ALREADY_ADDED);
      return false;
    }
    MainUtil.sendMessage(plr,C.HELPER_ADDED);
    return true;
  }
 else   if (args[0].equalsIgnoreCase("String_Node_Str")) {
    if (args[1].equalsIgnoreCase("String_Node_Str")) {
      final UUID uuid=DBFunc.everyone;
      if (!plot.helpers.contains(uuid)) {
        MainUtil.sendMessage(plr,C.WAS_NOT_ADDED);
        return true;
      }
      plot.removeHelper(uuid);
      DBFunc.removeHelper(loc.getWorld(),plot,uuid);
      MainUtil.sendMessage(plr,C.HELPER_REMOVED);
      return true;
    }
    final UUID uuid=UUIDHandler.getUUID(args[1]);
    plot.removeHelper(uuid);
    DBFunc.removeHelper(loc.getWorld(),plot,uuid);
    EventUtil.manager.callHelper(plr,plot,uuid,false);
    MainUtil.sendMessage(plr,C.HELPER_REMOVED);
  }
 else {
    MainUtil.sendMessage(plr,C.HELPER_NEED_ARGUMENT);
    return true;
  }
  return true;
}

Fixed version (ground truth):
@Override public boolean execute(final PlotPlayer plr,final String... args){
  if (args.length < 2) {
    MainUtil.sendMessage(plr,C.HELPER_NEED_ARGUMENT);
    return true;
  }
  final Location loc=plr.getLocation();
  final Plot plot=MainUtil.getPlot(loc);
  if (plot == null) {
    return !sendMessage(plr,C.NOT_IN_PLOT);
  }
  if ((plot == null) || !plot.hasOwner()) {
    MainUtil.sendMessage(plr,C.PLOT_UNOWNED);
    return false;
  }
  if (!plot.isOwner(plr.getUUID()) && !Permissions.hasPermission(plr,"String_Node_Str")) {
    MainUtil.sendMessage(plr,C.NO_PLOT_PERMS);
    return true;
  }
  if (args[0].equalsIgnoreCase("String_Node_Str")) {
    UUID uuid;
    if (args[1].equalsIgnoreCase("String_Node_Str")) {
      uuid=DBFunc.everyone;
    }
 else {
      uuid=UUIDHandler.getUUID(args[1]);
    }
    if (uuid == null) {
      MainUtil.sendMessage(plr,C.INVALID_PLAYER,args[1]);
      return false;
    }
    if (!plot.helpers.contains(uuid)) {
      if (plot.isOwner(uuid)) {
        MainUtil.sendMessage(plr,C.ALREADY_OWNER);
        return false;
      }
      if (plot.trusted.contains(uuid)) {
        plot.trusted.remove(uuid);
        DBFunc.removeTrusted(loc.getWorld(),plot,uuid);
      }
      if (plot.denied.contains(uuid)) {
        plot.denied.remove(uuid);
        DBFunc.removeDenied(loc.getWorld(),plot,uuid);
      }
      plot.addHelper(uuid);
      DBFunc.setHelper(loc.getWorld(),plot,uuid);
      EventUtil.manager.callHelper(plr,plot,uuid,true);
    }
 else {
      MainUtil.sendMessage(plr,C.ALREADY_ADDED);
      return false;
    }
    MainUtil.sendMessage(plr,C.HELPER_ADDED);
    return true;
  }
 else   if (args[0].equalsIgnoreCase("String_Node_Str")) {
    if (args[1].equalsIgnoreCase("String_Node_Str")) {
      final UUID uuid=DBFunc.everyone;
      if (!plot.helpers.contains(uuid)) {
        MainUtil.sendMessage(plr,C.WAS_NOT_ADDED);
        return true;
      }
      plot.removeHelper(uuid);
      DBFunc.removeHelper(loc.getWorld(),plot,uuid);
      MainUtil.sendMessage(plr,C.HELPER_REMOVED);
      return true;
    }
    final UUID uuid=UUIDHandler.getUUID(args[1]);
    plot.removeHelper(uuid);
    DBFunc.removeHelper(loc.getWorld(),plot,uuid);
    EventUtil.manager.callHelper(plr,plot,uuid,false);
    MainUtil.sendMessage(plr,C.HELPER_REMOVED);
  }
 else {
    MainUtil.sendMessage(plr,C.HELPER_NEED_ARGUMENT);
    return true;
  }
  return true;
}