Error handling with Spring MVC and ThymeLeaf

I'm doing an error trapping with @ExceptionHandler but I'm not able to make this information available in the View.

Example I'm doing a group register. If the group already exists it throws an error. This error is handled and returns a ModelAndView. But I can not make the message available in $ {# fields.detailedErrors ()} of thymeleaf.

What am I doing?

First I created a RuntimeException extending error class.

public class GrupoRoleJaCadastradaException extends RuntimeException {

    private static final long serialVersionUID = 1L;

    private Grupo grupo;
    private BindingResult result;

    public GrupoRoleJaCadastradaException(Grupo grupo,BindingResult result){
        super();
        this.grupo = grupo;
        this.result = result;
    }

    public GrupoRoleJaCadastradaException(Grupo grupo,BindingResult result,String message){
        super();
        this.grupo = grupo;
        this.result = result;
    }

    public Grupo getGrupo() {
        return grupo;
    }

    public BindingResult getResult() {
        return result;
    }

}

Do not control when calling the service sending the Group object and the BindingResult where I will do the treatment.

@PostMapping("/grupos/novo")
    public ModelAndView salvarNovo(@Valid Grupo grupo, BindingResult result, Model model,RedirectAttributes attributes,@AuthenticationPrincipal UsuarioSistema usuarioSistema ) {



        if(result.hasErrors()){
            return novoGrupo(grupo);
        }
            grupo = grupoService.salvar(grupo,result);

            attributes.addFlashAttribute("mensagem", "Grupo salvo com sucesso");
            return new ModelAndView("redirect:/administracao/grupos");

    }

In Service I'm releasing the created error

public Grupo salvar(Grupo grupo, BindingResult result) {
        throw new GrupoRoleJaCadastradaException(grupo,result);

        //return grupoRep.save(grupo);

    }

On the Controller, I intercept the posted error

@ExceptionHandler({GrupoRoleJaCadastradaException.class})
    public ModelAndView handlerGrupoRoleJaCadastradaException(GrupoRoleJaCadastradaException ex){

        grupoValidator.validate(ex.getGrupo(), ex.getResult() );

        return novoGrupo(ex.getGrupo());
}

In the GroupValidator class I treat the error

@Override
    public void validate(Object target, Errors errors) {
        errors.rejectValue("role", " ", "teste de erro validate" );

    }

And return a ModelAndView that shows the screen. - return newGroup (ex.Group ());

But the error does not reach the view.

I have tried several alternatives like adding the BindingResult object to the ModelAndView as below but it also did not work.

@ExceptionHandler({GrupoRoleJaCadastradaException.class})
public ModelAndView handlerGrupoRoleJaCadastradaException(GrupoRoleJaCadastradaException ex){

        grupoValidator.validate(ex.getGrupo(), ex.getResult() );

        return novoGrupo(ex.getGrupo(), ex.getResult());
}


private ModelAndView novoGrupo(Grupo grupo) {
    ModelAndView mv = new ModelAndView("administracao/GrupoCadastro");
    mv.addObject("grupo", grupo);
    return mv;
}

private ModelAndView novoGrupo(Grupo grupo,BindingResult result) {
    System.out.println("-----"+result);
    return novo(grupo).addObject(result);
}

Note that I gave a sysout in the result and make sure the error is there.

But when displaying the page there is no error.

<H1>[[${#fields.hasAnyErrors()}]]</H1>
<div class="alert  alert-danger  alert-dismissible" role="alert" th:if="${#fields.hasAnyErrors()}"  >
    <button type="button" class="close" data-dismiss="alert"><span aria-hidden="true">&times;</span></button>
    <th:block th:each="detailedError : ${#fields.detailedErrors()}">
        <div><i class="fa  fa-exclamation-circle"></i> [[${detailedError.message}]]</div>
    </th:block>
</div>