Error running Servlet Nullpointerexception

Question

Hello, create a Servlet to be able to make changes to users registered in the bd. In this excerpt I try to recover the employee data by id and redirect to the change page:

    @Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    try{
        int id = Integer.parseInt(request.getParameter("id"));
        ClienteDAO dao = new ClienteDAO();
        Cliente cliente = dao.getClientePorCodigo(id);
        if(cliente.getId() > 0 ){
            RequestDispatcher disp = getServletContext().getRequestDispatcher("/funcionario/Paginas/cadastrar.jsp");
            request.setAttribute("clientes", cliente);
            disp.forward(request, response);

        }
        else{
            PrintWriter out = response.getWriter();
            out.println("<script>alert('Usuário não encontrado!'); location.href = 'funcionario/Paginas/dashboard.jsp'</script>");
        }   
    }
    catch( IOException | NumberFormatException | ServletException e ){
        System.out.println("Erro ao recuperar dados");
        System.out.println("Erro: " + e.getMessage());
    }
}

but when I run the page is empty:

Would anyone know where this mistake of mine?