Program: 1902
Project: 1902
Buggy source:
@Override public boolean onCommand(CommandSender sender,Command command,String commandLabel,String[] args){
  if (!(sender instanceof Player)) {
    sender.sendMessage(MessageUtils.mustBeIngameMessage);
    return true;
  }
  Player player=(Player)sender;
  HumanNPC npc=null;
  boolean returnval=false;
  if (NPCManager.validateSelected((Player)sender)) {
    npc=NPCManager.get(NPCManager.selectedNPCs.get(player.getName()));
  }
 else {
    sender.sendMessage(MessageUtils.mustHaveNPCSelectedMessage);
    return true;
  }
  if (!NPCManager.validateOwnership(player,npc.getUID())) {
    sender.sendMessage(MessageUtils.notOwnerMessage);
    return true;
  }
  if (!npc.isQuester()) {
    sender.sendMessage(ChatColor.RED + "String_Node_Str");
    return true;
  }
 else {
    if (args.length == 1 && args[0].equalsIgnoreCase("String_Node_Str")) {
      if (Permission.canUse(player,npc,"String_Node_Str")) {
        HelpUtils.sendQuesterHelp(sender);
      }
 else {
        sender.sendMessage(MessageUtils.noPermissionsMessage);
      }
      return true;
    }
 else     if (args.length == 2 && args[0].contains("String_Node_Str")) {
      if (Permission.canModify(player,npc,"String_Node_Str")) {
        assignQuest(player,npc,args[1]);
      }
 else {
        sender.sendMessage(MessageUtils.noPermissionsMessage);
      }
      returnval=true;
    }
 else     if (args.length == 2 && args[0].contains("String_Node_Str")) {
      if (Permission.canModify(player,npc,"String_Node_Str")) {
        removeQuest(player,npc,args[1]);
      }
 else {
        sender.sendMessage(MessageUtils.noPermissionsMessage);
      }
      returnval=true;
    }
    PropertyManager.save(npc);
  }
  return returnval;
}

Fixed version (ground truth):
@Override public boolean onCommand(CommandSender sender,Command command,String commandLabel,String[] args){
  if (!(sender instanceof Player)) {
    sender.sendMessage(MessageUtils.mustBeIngameMessage);
    return true;
  }
  Player player=(Player)sender;
  HumanNPC npc=null;
  boolean returnval=false;
  if (NPCManager.validateSelected((Player)sender)) {
    npc=NPCManager.get(NPCManager.selectedNPCs.get(player.getName()));
  }
 else {
    sender.sendMessage(MessageUtils.mustHaveNPCSelectedMessage);
    return true;
  }
  if (!NPCManager.validateOwnership(player,npc.getUID())) {
    sender.sendMessage(MessageUtils.notOwnerMessage);
    return true;
  }
  if (!npc.isQuester()) {
    sender.sendMessage(ChatColor.RED + "String_Node_Str");
    return true;
  }
 else {
    if (args.length == 1 && args[0].equalsIgnoreCase("String_Node_Str")) {
      if (Permission.canHelp(player,npc,"String_Node_Str")) {
        HelpUtils.sendQuesterHelp(sender);
      }
 else {
        sender.sendMessage(MessageUtils.noPermissionsMessage);
      }
      return true;
    }
 else     if (args.length == 2 && args[0].contains("String_Node_Str")) {
      if (Permission.canModify(player,npc,"String_Node_Str")) {
        assignQuest(player,npc,args[1]);
      }
 else {
        sender.sendMessage(MessageUtils.noPermissionsMessage);
      }
      returnval=true;
    }
 else     if (args.length == 2 && args[0].contains("String_Node_Str")) {
      if (Permission.canModify(player,npc,"String_Node_Str")) {
        removeQuest(player,npc,args[1]);
      }
 else {
        sender.sendMessage(MessageUtils.noPermissionsMessage);
      }
      returnval=true;
    }
    PropertyManager.save(npc);
  }
  return returnval;
}