Duvida com método update

Pessoal, estou tentando criar um método para editar. Tenho uma classe Nivel que é a minha entidade:

 @Entity
 @Table(name="niveis")
public class Nivel extends AbstractPersistable<Long> {    

private static final long serialVersionUID = 1L;

@NotBlank(message="Campo obrigatório.")
@Length(min = 3, max = 50)
@Column(nullable = false, unique = true, length = 50)
private String nome;

public String getNome() {
    return nome;
}

public void setNome(String nome) {
    this.nome = nome;
}

@Override
protected void setId(Long id) {
    super.setId(id);
}}

Aqui está o Repository:

public interface NivelRepository extends JpaRepository<Nivel, Long>{

Page<Nivel> findAllByOrderByNomeAsc(Pageable pageable);
List<Nivel> findAll();
Nivel findOne(Long id);
Nivel findByNome(String nome);

@Modifying
@Query("update Nivel n set n.nome = ?1 where n.id = ?2")
void updateNome(String nome, Long id); 

}

O service ficou assim:

@Service
@Transactional(readOnly=true, propagation =      
       Propagation.REQUIRED)public class NivelService {

@Autowired
private NivelRepository repository;

public Page<Nivel> findByPagination(int page, int size) {
    Pageable pageable = new PageRequest(page, size);
    return repository.findAllByOrderByNomeAsc(pageable);
}

 public List<Nivel> findAll() {

    return repository.findAll();
}

public Nivel findByNome(String nome) {

    return repository.findByNome(nome);
}

public Nivel findById(Long id) {

    return repository.findOne(id);
}

@Transactional(readOnly = false)
public void delete(Long id) {

    repository.delete(id);        
}

@Transactional(readOnly = false)
public void saveOrUpdate(Nivel nivel) {
    if (nivel.getId() == null) {
        save(nivel);
    } else {
        update(nivel);
    }
}

    private void update(Nivel nivel) {

    Nivel persistente = repository.findOne(nivel.getId());

    if (!persistente.getNome().equals(nivel.getNome())) {
        persistente.setNome(nivel.getNome());
    }

    repository.save(persistente);
 }

private void save (Nivel nivel) {
repository.save(nivel);

}

 }

O meu controller ficou desta forma:

@Controller
@RequestMapping(value="nivel")
    public class NivelController {

@Autowired
private NivelService nivelService;


@RequestMapping(value = "/page/{page}", method = RequestMethod.GET)
public ModelAndView pageNiveis(@PathVariable("page") Integer pagina) {
    ModelAndView view = new ModelAndView("nivel/list");

    Page<Nivel> page = nivelService.findByPagination(pagina - 1, 5);

    view.addObject("page", page);
    view.addObject("urlPagination", "/nivel/page");

    return view;
}

@RequestMapping(value = "/delete/{id}", method = RequestMethod.GET)
public String delete(@PathVariable("id") Long id) {

    nivelService.delete(id);

    return "redirect:/nivel/add";
}

@RequestMapping(value="/update/{id}", method=RequestMethod.GET)
public ModelAndView preUpdate(@PathVariable("id") Long id, ModelMap model) {
    Nivel nivel = nivelService.findById(id);
    model.addAttribute("nivel", nivel);
    return new ModelAndView("/nivel/cadastro", model);
}

@RequestMapping(value="/update", method=RequestMethod.POST)
public ModelAndView update(@Valid @ModelAttribute("nivel") Nivel nivel, BindingResult result, RedirectAttributes attr) {
    if (result.hasErrors()) {
        return new ModelAndView("/nivel/cadastro");
    }
    nivelService.saveOrUpdate(nivel);

    attr.addFlashAttribute("message", "Nível alterado com sucesso.");
    return new ModelAndView("redirect:/nivel/list");
}
@RequestMapping(value = {"/nivel/{id}", "/list"}, method = RequestMethod.GET)
public ModelAndView getNivel(@PathVariable("id") Optional<Long> id) {

    ModelAndView view = new ModelAndView("nivel/list");

    if (id.isPresent()) {

        Nivel nivel = nivelService.findById(id.get());        
        view.addObject("niveis", Arrays.asList(nivel));
    } else {

        List<Nivel> niveis = nivelService.findAll();
        view.addObject("niveis", niveis);
        Page<Nivel> page = nivelService.findByPagination(0, 5);
        view.addObject("page", page);
        view.addObject("urlPagination", "/nivel/page");
    }

    return view;                
}

@RequestMapping(value = "/save", method = RequestMethod.POST)
public ModelAndView save(@ModelAttribute("nivel") @Validated Nivel nivel, BindingResult result) {

    ModelAndView view = new ModelAndView();

    if ( result.hasErrors() ) {

        Page<Nivel> page = nivelService.findByPagination(0, 5);

        view.addObject("page", page);
        view.addObject("urlPagination", "/categoria/page");
        view.setViewName("categoria/cadastro");

        return view;
    }

    nivelService.saveOrUpdate(nivel);

    view.setViewName("redirect:/nivel/add");

    return view;
     }    
}