Program: 51665
Project: 51665
Buggy source:
@EventHandler public void onNPCRightCLick(NPCRightClickEvent event){
  if (!isEconomyNpc(event.getNPC()))   return;
  Player player=event.getClicker();
  final String playerName=player.getName();
  NPC npc=event.getNPC();
  EconomyNpc economyNpc=playerInteraction.get(playerName);
  TraderCharacterTrait characterTrait=npc.getTrait(TraderCharacterTrait.class);
  if (economyNpc != null) {
    if (player.getItemInHand().getTypeId() == config.getMMToggleItem().getTypeId()) {
      if ((permManager.has(player,"String_Node_Str") && characterTrait.getTraderTrait().getOwner().equals(player.getName())) || permManager.has(player,"String_Node_Str") || player.isOp()) {
        if (economyNpc.getNpcId() == npc.getId()) {
          playerInteraction.remove(playerName);
          player.sendMessage(ChatColor.AQUA + npc.getFullName() + ChatColor.RED+ "String_Node_Str");
          return;
        }
        if (!permManager.has(player,"String_Node_Str" + characterTrait.getTraderType().toString())) {
          player.sendMessage(locale.getLocaleString("String_Node_Str"));
          return;
        }
        if (player.getGameMode().equals(GameMode.CREATIVE) && !permManager.has(player,"String_Node_Str")) {
          player.sendMessage(locale.getLocaleString("String_Node_Str"));
          return;
        }
        if (characterTrait.getTraderType().equals(TraderType.PLAYER_TRADER)) {
          playerInteraction.put(playerName,new PlayerTrader(npc,characterTrait.getTraderTrait()));
        }
        if (characterTrait.getTraderType().equals(TraderType.SERVER_TRADER)) {
          playerInteraction.put(playerName,new ServerTrader(npc,characterTrait.getTraderTrait()));
        }
        playerInteraction.get(playerName).setTraderStatus(TraderStatus.MANAGE);
        player.sendMessage(ChatColor.AQUA + npc.getFullName() + ChatColor.RED+ "String_Node_Str");
        return;
      }
      return;
    }
    if (economyNpc.getNpcId() == npc.getId()) {
      player.openInventory(playerInteraction.get(playerName).getInventory());
      return;
    }
    if (!TraderStatus.hasManageMode(playerInteraction.get(playerName).getTraderStatus()))     return;
    player.sendMessage(ChatColor.AQUA + CitizensAPI.getNPCRegistry().getById(economyNpc.getNpcId()).getFullName() + ChatColor.RED+ "String_Node_Str");
    playerInteraction.get(playerName).setTraderStatus(TraderStatus.SELL);
    player.openInventory(playerInteraction.get(playerName).getInventory());
    return;
  }
  if (player.getItemInHand().getTypeId() == config.getMMToggleItem().getTypeId()) {
    if ((permManager.has(player,"String_Node_Str") && characterTrait.getTraderTrait().getOwner().equals(player.getName())) || permManager.has(player,"String_Node_Str") || player.isOp()) {
      if (!permManager.has(player,"String_Node_Str" + characterTrait.getTraderType().toString())) {
        player.sendMessage(locale.getLocaleString("String_Node_Str"));
        return;
      }
      if (player.getGameMode().equals(GameMode.CREATIVE) && !permManager.has(player,"String_Node_Str")) {
        player.sendMessage(locale.getLocaleString("String_Node_Str"));
        return;
      }
      if (characterTrait.getTraderType().equals(TraderType.PLAYER_TRADER)) {
        playerInteraction.put(playerName,new PlayerTrader(npc,characterTrait.getTraderTrait()));
      }
      if (characterTrait.getTraderType().equals(TraderType.SERVER_TRADER)) {
        playerInteraction.put(playerName,new ServerTrader(npc,characterTrait.getTraderTrait()));
      }
      playerInteraction.get(playerName).setTraderStatus(TraderStatus.MANAGE);
      player.sendMessage(ChatColor.AQUA + npc.getFullName() + ChatColor.RED+ "String_Node_Str");
      return;
    }
    return;
  }
  player.openInventory(playerInteraction.get(playerName).getInventory());
}

Fixed version (ground truth):
@EventHandler public void onNPCRightCLick(NPCRightClickEvent event){
  if (!isEconomyNpc(event.getNPC()))   return;
  Player player=event.getClicker();
  final String playerName=player.getName();
  NPC npc=event.getNPC();
  EconomyNpc economyNpc=playerInteraction.get(playerName);
  TraderCharacterTrait characterTrait=npc.getTrait(TraderCharacterTrait.class);
  if (economyNpc != null) {
    if (player.getItemInHand().getTypeId() == config.getMMToggleItem().getTypeId()) {
      if ((permManager.has(player,"String_Node_Str") && characterTrait.getTraderTrait().getOwner().equals(player.getName())) || permManager.has(player,"String_Node_Str") || player.isOp()) {
        if (economyNpc.getNpcId() == npc.getId()) {
          playerInteraction.remove(playerName);
          player.sendMessage(ChatColor.AQUA + npc.getFullName() + ChatColor.RED+ "String_Node_Str");
          return;
        }
        if (!permManager.has(player,"String_Node_Str" + characterTrait.getTraderType().toString())) {
          player.sendMessage(locale.getLocaleString("String_Node_Str"));
          return;
        }
        if (player.getGameMode().equals(GameMode.CREATIVE) && !permManager.has(player,"String_Node_Str")) {
          player.sendMessage(locale.getLocaleString("String_Node_Str"));
          return;
        }
        if (characterTrait.getTraderType().equals(TraderType.PLAYER_TRADER)) {
          playerInteraction.put(playerName,new PlayerTrader(npc,characterTrait.getTraderTrait()));
        }
        if (characterTrait.getTraderType().equals(TraderType.SERVER_TRADER)) {
          playerInteraction.put(playerName,new ServerTrader(npc,characterTrait.getTraderTrait()));
        }
        playerInteraction.get(playerName).setTraderStatus(TraderStatus.MANAGE);
        player.sendMessage(ChatColor.AQUA + npc.getFullName() + ChatColor.RED+ "String_Node_Str");
        return;
      }
      return;
    }
    if (economyNpc.getNpcId() == npc.getId()) {
      ((Trader)playerInteraction.get(playerName)).switchInventory(TraderStatus.MANAGE_SELL);
      player.openInventory(playerInteraction.get(playerName).getInventory());
      return;
    }
    if (!TraderStatus.hasManageMode(playerInteraction.get(playerName).getTraderStatus()))     return;
    player.sendMessage(ChatColor.AQUA + CitizensAPI.getNPCRegistry().getById(economyNpc.getNpcId()).getFullName() + ChatColor.RED+ "String_Node_Str");
    if (characterTrait.getTraderType().equals(TraderType.PLAYER_TRADER)) {
      playerInteraction.put(playerName,new PlayerTrader(npc,characterTrait.getTraderTrait()));
    }
    if (characterTrait.getTraderType().equals(TraderType.SERVER_TRADER)) {
      playerInteraction.put(playerName,new ServerTrader(npc,characterTrait.getTraderTrait()));
    }
    player.openInventory(playerInteraction.get(playerName).getInventory());
    return;
  }
  if (player.getItemInHand().getTypeId() == config.getMMToggleItem().getTypeId()) {
    if ((permManager.has(player,"String_Node_Str") && characterTrait.getTraderTrait().getOwner().equals(player.getName())) || permManager.has(player,"String_Node_Str") || player.isOp()) {
      if (!permManager.has(player,"String_Node_Str" + characterTrait.getTraderType().toString())) {
        player.sendMessage(locale.getLocaleString("String_Node_Str"));
        return;
      }
      if (player.getGameMode().equals(GameMode.CREATIVE) && !permManager.has(player,"String_Node_Str")) {
        player.sendMessage(locale.getLocaleString("String_Node_Str"));
        return;
      }
      if (characterTrait.getTraderType().equals(TraderType.PLAYER_TRADER)) {
        playerInteraction.put(playerName,new PlayerTrader(npc,characterTrait.getTraderTrait()));
      }
      if (characterTrait.getTraderType().equals(TraderType.SERVER_TRADER)) {
        playerInteraction.put(playerName,new ServerTrader(npc,characterTrait.getTraderTrait()));
      }
      playerInteraction.get(playerName).setTraderStatus(TraderStatus.MANAGE);
      player.sendMessage(ChatColor.AQUA + npc.getFullName() + ChatColor.RED+ "String_Node_Str");
      return;
    }
    return;
  }
  if (!permManager.has(player,"String_Node_Str" + characterTrait.getTraderType().toString())) {
    player.sendMessage(locale.getLocaleString("String_Node_Str"));
    return;
  }
  if (player.getGameMode().equals(GameMode.CREATIVE) && !permManager.has(player,"String_Node_Str")) {
    player.sendMessage(locale.getLocaleString("String_Node_Str"));
    return;
  }
  if (characterTrait.getTraderType().equals(TraderType.PLAYER_TRADER)) {
    playerInteraction.put(playerName,new PlayerTrader(npc,characterTrait.getTraderTrait()));
  }
  if (characterTrait.getTraderType().equals(TraderType.SERVER_TRADER)) {
    playerInteraction.put(playerName,new ServerTrader(npc,characterTrait.getTraderTrait()));
  }
  if (characterTrait.getTraderType().equals(TraderType.PLAYER_BANK)) {
    playerInteraction.put(playerName,new PlayerBanker(npc,characterTrait.getBankTrait()));
  }
  player.openInventory(playerInteraction.get(playerName).getInventory());
}