Program: 58158
Project: 58158
Buggy source:
@Override public boolean execute(Player plr,String... args){
  if (args.length < 2) {
    PlayerFunctions.sendMessage(plr,C.HELPER_NEED_ARGUMENT);
    return true;
  }
  if (!PlayerFunctions.isInPlot(plr)) {
    PlayerFunctions.sendMessage(plr,C.NOT_IN_PLOT);
    return true;
  }
  Plot plot=PlayerFunctions.getCurrentPlot(plr);
  if ((plot.owner == null) || !plot.hasRights(plr)) {
    PlayerFunctions.sendMessage(plr,C.NO_PERMISSION);
    return true;
  }
  if (args[0].equalsIgnoreCase("String_Node_Str")) {
    if (args[1].equalsIgnoreCase("String_Node_Str")) {
      UUID uuid=DBFunc.everyone;
      plot.addHelper(uuid);
      DBFunc.setHelper(plr.getWorld().getName(),plot,Bukkit.getOfflinePlayer(args[1]));
      PlayerFunctions.sendMessage(plr,C.HELPER_ADDED);
      return true;
    }
    if (!hasBeenOnServer(args[1])) {
      PlayerFunctions.sendMessage(plr,C.PLAYER_HAS_NOT_BEEN_ON);
      return true;
    }
    UUID uuid=null;
    if ((Bukkit.getPlayerExact(args[1]) != null)) {
      uuid=Bukkit.getPlayerExact(args[1]).getUniqueId();
    }
 else {
      uuid=Bukkit.getOfflinePlayer(args[1]).getUniqueId();
    }
    if (uuid == null) {
      PlayerFunctions.sendMessage(plr,C.PLAYER_HAS_NOT_BEEN_ON);
      return true;
    }
    plot.addHelper(uuid);
    DBFunc.setHelper(plr.getWorld().getName(),plot,Bukkit.getOfflinePlayer(args[1]));
    PlayerPlotHelperEvent event=new PlayerPlotHelperEvent(plr,plot,uuid,true);
    Bukkit.getPluginManager().callEvent(event);
    PlayerFunctions.sendMessage(plr,C.HELPER_ADDED);
  }
 else   if (args[0].equalsIgnoreCase("String_Node_Str")) {
    if (args[1].equalsIgnoreCase("String_Node_Str")) {
      UUID uuid=DBFunc.everyone;
      if (!plot.helpers.contains(uuid)) {
        PlayerFunctions.sendMessage(plr,C.WAS_NOT_ADDED);
        return true;
      }
      plot.removeHelper(uuid);
      DBFunc.removeHelper(plr.getWorld().getName(),plot,Bukkit.getOfflinePlayer(args[1]));
      PlayerFunctions.sendMessage(plr,C.HELPER_REMOVED);
      return true;
    }
    if (!hasBeenOnServer(args[1])) {
      PlayerFunctions.sendMessage(plr,C.PLAYER_HAS_NOT_BEEN_ON);
      return true;
    }
    UUID uuid=null;
    if (Bukkit.getPlayerExact(args[1]) != null) {
      uuid=Bukkit.getPlayerExact(args[1]).getUniqueId();
    }
 else {
      uuid=Bukkit.getOfflinePlayer(args[1]).getUniqueId();
    }
    if (uuid == null) {
      PlayerFunctions.sendMessage(plr,C.PLAYER_HAS_NOT_BEEN_ON);
      return true;
    }
    if (!plot.helpers.contains(uuid)) {
      PlayerFunctions.sendMessage(plr,C.WAS_NOT_ADDED);
      return true;
    }
    plot.removeHelper(uuid);
    DBFunc.removeHelper(plr.getWorld().getName(),plot,Bukkit.getOfflinePlayer(args[1]));
    PlayerPlotHelperEvent event=new PlayerPlotHelperEvent(plr,plot,uuid,false);
    Bukkit.getPluginManager().callEvent(event);
    PlayerFunctions.sendMessage(plr,C.HELPER_REMOVED);
  }
 else {
    PlayerFunctions.sendMessage(plr,C.HELPER_NEED_ARGUMENT);
    return true;
  }
  return true;
}

Fixed version (ground truth):
@Override public boolean execute(Player plr,String... args){
  if (args.length < 2) {
    PlayerFunctions.sendMessage(plr,C.HELPER_NEED_ARGUMENT);
    return true;
  }
  if (!PlayerFunctions.isInPlot(plr)) {
    PlayerFunctions.sendMessage(plr,C.NOT_IN_PLOT);
    return true;
  }
  Plot plot=PlayerFunctions.getCurrentPlot(plr);
  if ((plot.owner == null) || !plot.hasRights(plr)) {
    PlayerFunctions.sendMessage(plr,C.NO_PERMISSION);
    return true;
  }
  if (args[0].equalsIgnoreCase("String_Node_Str")) {
    if (args[1].equalsIgnoreCase("String_Node_Str")) {
      UUID uuid=DBFunc.everyone;
      plot.addHelper(uuid);
      DBFunc.setHelper(plr.getWorld().getName(),plot,Bukkit.getOfflinePlayer(args[1]));
      PlayerFunctions.sendMessage(plr,C.HELPER_ADDED);
      return true;
    }
    if (!hasBeenOnServer(args[1])) {
      PlayerFunctions.sendMessage(plr,C.PLAYER_HAS_NOT_BEEN_ON);
      return true;
    }
    UUID uuid=null;
    if ((Bukkit.getPlayer(args[1]) != null)) {
      uuid=Bukkit.getPlayer(args[1]).getUniqueId();
    }
 else {
      uuid=Bukkit.getOfflinePlayer(args[1]).getUniqueId();
    }
    if (uuid == null) {
      PlayerFunctions.sendMessage(plr,C.PLAYER_HAS_NOT_BEEN_ON);
      return true;
    }
    plot.addHelper(uuid);
    DBFunc.setHelper(plr.getWorld().getName(),plot,Bukkit.getOfflinePlayer(args[1]));
    PlayerPlotHelperEvent event=new PlayerPlotHelperEvent(plr,plot,uuid,true);
    Bukkit.getPluginManager().callEvent(event);
    PlayerFunctions.sendMessage(plr,C.HELPER_ADDED);
  }
 else   if (args[0].equalsIgnoreCase("String_Node_Str")) {
    if (args[1].equalsIgnoreCase("String_Node_Str")) {
      UUID uuid=DBFunc.everyone;
      if (!plot.helpers.contains(uuid)) {
        PlayerFunctions.sendMessage(plr,C.WAS_NOT_ADDED);
        return true;
      }
      plot.removeHelper(uuid);
      DBFunc.removeHelper(plr.getWorld().getName(),plot,Bukkit.getOfflinePlayer(args[1]));
      PlayerFunctions.sendMessage(plr,C.HELPER_REMOVED);
      return true;
    }
    if (!hasBeenOnServer(args[1])) {
      PlayerFunctions.sendMessage(plr,C.PLAYER_HAS_NOT_BEEN_ON);
      return true;
    }
    UUID uuid=null;
    if (Bukkit.getPlayer(args[1]) != null) {
      uuid=Bukkit.getPlayer(args[1]).getUniqueId();
    }
 else {
      uuid=Bukkit.getOfflinePlayer(args[1]).getUniqueId();
    }
    if (uuid == null) {
      PlayerFunctions.sendMessage(plr,C.PLAYER_HAS_NOT_BEEN_ON);
      return true;
    }
    if (!plot.helpers.contains(uuid)) {
      PlayerFunctions.sendMessage(plr,C.WAS_NOT_ADDED);
      return true;
    }
    plot.removeHelper(uuid);
    DBFunc.removeHelper(plr.getWorld().getName(),plot,Bukkit.getOfflinePlayer(args[1]));
    PlayerPlotHelperEvent event=new PlayerPlotHelperEvent(plr,plot,uuid,false);
    Bukkit.getPluginManager().callEvent(event);
    PlayerFunctions.sendMessage(plr,C.HELPER_REMOVED);
  }
 else {
    PlayerFunctions.sendMessage(plr,C.HELPER_NEED_ARGUMENT);
    return true;
  }
  return true;
}