Program: 1993
Project: 1993
Buggy source:
@Override public void onEntityTarget(EntityTargetEvent event){
  if (!(event instanceof NPCEntityTargetEvent))   return;
  NPCEntityTargetEvent e=(NPCEntityTargetEvent)event;
  HumanNPC npc=NPCManager.getNPC(e.getEntity());
  if (NPCManager.getNPC(e.getTarget()) != null) {
    if (e.getEntity() instanceof Monster && !(e.getEntity() instanceof Player))     e.setCancelled(true);
  }
  if (npc != null && event.getTarget() instanceof Player) {
    if (e.getNpcReason() == NpcTargetReason.NPC_RIGHTCLICKED) {
      Player p=(Player)event.getTarget();
      boolean found=false;
      if (plugin.validateTool("String_Node_Str",p.getItemInHand().getTypeId()) == true) {
        CitizensBasicNPCEvent ev=new CitizensBasicNPCEvent(npc.getName(),MessageUtils.getText(npc,(Player)e.getTarget(),plugin),npc,Reason.RIGHT_CLICK,(Player)e.getTarget());
        plugin.getServer().getPluginManager().callEvent(ev);
        found=true;
      }
      if (npc.isTrader()) {
        TraderInterface.handleRightClick(npc,p);
        found=true;
      }
      if (npc.isWizard()) {
        if (Permission.hasPermission("String_Node_Str",(CommandSender)p)) {
          if (p.getItemInHand().getTypeId() == Citizens.wizardInteractItem) {
            if (npc.getWizard().getNrOfLocations() > 0) {
              this.buyTeleport(p,npc.getWizard(),Operation.WIZARD_TELEPORT);
              found=true;
            }
          }
        }
 else {
          p.sendMessage(MessageUtils.noPermissionsMessage);
        }
      }
      if (npc.isBlacksmith()) {
        if (Permission.hasPermission("String_Node_Str",(CommandSender)p)) {
          buyToolRepair(p,npc,Operation.BLACKSMITH_TOOL_REPAIR);
          found=true;
        }
 else {
          p.sendMessage(MessageUtils.noPermissionsMessage);
        }
      }
      if (found && !plugin.canSelectAny())       return;
      if (plugin.validateTool("String_Node_Str",p.getItemInHand().getTypeId()) == true) {
        if (!NPCManager.validateSelected(p,npc.getUID())) {
          NPCManager.NPCSelected.put(p.getName(),npc.getUID());
          p.sendMessage(ChatColor.GREEN + "String_Node_Str" + StringUtils.yellowify(npc.getStrippedName())+ "String_Node_Str"+ StringUtils.yellowify("String_Node_Str" + npc.getUID())+ "String_Node_Str");
        }
 else         if (!found && plugin.canSelectAny()) {
          p.sendMessage(ChatColor.GREEN + "String_Node_Str");
        }
      }
    }
  }
}

Fixed version (ground truth):
@Override public void onEntityTarget(EntityTargetEvent event){
  if (!(event instanceof NPCEntityTargetEvent))   return;
  NPCEntityTargetEvent e=(NPCEntityTargetEvent)event;
  HumanNPC npc=NPCManager.getNPC(e.getEntity());
  if (NPCManager.getNPC(e.getTarget()) != null) {
    if (e.getEntity() instanceof Monster && !(e.getEntity() instanceof Player))     e.setCancelled(true);
  }
  if (npc != null && event.getTarget() instanceof Player) {
    if (e.getNpcReason() == NpcTargetReason.NPC_RIGHTCLICKED) {
      Player p=(Player)event.getTarget();
      if (plugin.validateTool("String_Node_Str",p.getItemInHand().getTypeId()) == true) {
        if (!NPCManager.validateSelected(p,npc.getUID())) {
          NPCManager.NPCSelected.put(p.getName(),npc.getUID());
          p.sendMessage(ChatColor.GREEN + "String_Node_Str" + StringUtils.yellowify(npc.getStrippedName())+ "String_Node_Str"+ StringUtils.yellowify("String_Node_Str" + npc.getUID())+ "String_Node_Str");
          return;
        }
      }
      if (plugin.validateTool("String_Node_Str",p.getItemInHand().getTypeId()) == true) {
        CitizensBasicNPCEvent ev=new CitizensBasicNPCEvent(npc.getName(),MessageUtils.getText(npc,(Player)e.getTarget(),plugin),npc,Reason.RIGHT_CLICK,(Player)e.getTarget());
        plugin.getServer().getPluginManager().callEvent(ev);
      }
      if (npc.isTrader()) {
        TraderInterface.handleRightClick(npc,p);
      }
      if (npc.isWizard()) {
        if (Permission.hasPermission("String_Node_Str",(CommandSender)p)) {
          if (p.getItemInHand().getTypeId() == Citizens.wizardInteractItem) {
            if (npc.getWizard().getNrOfLocations() > 0) {
              this.buyTeleport(p,npc.getWizard(),Operation.WIZARD_TELEPORT);
            }
          }
        }
 else {
          p.sendMessage(MessageUtils.noPermissionsMessage);
        }
      }
      if (npc.isBlacksmith()) {
        if (Permission.hasPermission("String_Node_Str",(CommandSender)p)) {
          buyToolRepair(p,npc,Operation.BLACKSMITH_TOOL_REPAIR);
        }
 else {
          p.sendMessage(MessageUtils.noPermissionsMessage);
        }
      }
    }
  }
}