@RequestMapping(value = "/{id}/control-letters", method = RequestMethod.GET)
  public String showControlLetters(
      @PathVariable("id") int id, Model model, final RedirectAttributes redirectAttributes) {
    if (!ticketsInvoiceService.invoiceExists(id)) throw new ResourceNotFoundException();

    List<ControlLetter> controlLetters = controlLetterService.findAll(id);
    handleFlashMessages(redirectAttributes, model);

    model.addAttribute("ticketsInvoiceId", id);
    model.addAttribute("controlLetters", controlLetters);

    return "controlLetter/find";
  }