SpringMVC. Redirect with errors

@Controller
public class ClientController implements Serializable {
 
    private List<Client> clients = new LinkedList<>();
 
    public ClientController() {
    }
 
    @RequestMapping(value = {"/index", "/"}, method = RequestMethod.GET)
    public String index(Model model, HttpServletRequest req) {
        if (!model.containsAttribute("client")) {
//            model.addAttribute("client", new Client("TLastname", "asd@email", "11-22-33", 99));
            model.addAttribute("client", new Client("TName", "TLastname", "asd@email.com", "11-22-33", 44));
        }
        model.addAttribute("cp", req.getContextPath());
        model.addAttribute("clients", clients);
        return "index";
    }
 
    @RequestMapping(value = "/client/save", method = RequestMethod.POST)
    public String save(
            @Valid @ModelAttribute("client") Client client,
            BindingResult result, Model model, RedirectAttributes att, HttpServletRequest req) {
        if (result.hasErrors()) {
            att.addFlashAttribute("client", client);
            return "redirect:/index";
        }
        clients.add(client);
        att.addFlashAttribute("message", client.getName() + " " + client.getLastname() + " was added!");
        return "redirect:/index";
    }

public class Client implements Serializable {
 
    @Email(message = "Email address is wrong")
    private String email;
    
    private String name;
    private String lastname;
    private String phone;
    private Integer age;
// SETTERS/GETTERS