Erros em Persit, merge e remove, help-me

private void mergeUsuario(Usuario usuario) {
        EntityManager em = null;
        Collection<Permissao> permOld = null;
        Collection<Permissao> permNew = null;
        try {
            em = getEntityManager();
            utx.begin();
            //usuario banco
            Usuario u = em.find(Usuario.class, usuario.getIdUsuario());
            //pega lista de rules do banco
            permOld = u.getPermissaoCollection();
            System.out.println(">>permOld: "+permOld.size());
            //pega lista de rules do formulario
            permNew = haveRules(usuario);
            System.out.println(">>permNew: "+permNew.size());
            
            
            for (Permissao p : permOld) {
                if (permNew.size()==0 || !areThereIn(permNew, p)) {
                    p = em.getReference(p.getClass(), p.getIdPermissao());
                    System.out.println(">>remover acesso: "+p.getAcesso()+" ,pk: "+p.getIdPermissao());
                    Usuario user = p.getUsuarioidUsuario();
                    user.getPermissaoCollection().remove(p);
                    user = em.merge(user);
                    em.remove(p);
                }
            }
            
            for (Permissao p : permNew) {
                if (!areThereIn(permOld, p)) {
                    em.persist(p);
                    Usuario user = p.getUsuarioidUsuario();
                    user.getPermissaoCollection().add(p);
                    user = em.merge(user);
                }
            }       
            
            utx.commit();
        } catch (Exception e) {
            e.printStackTrace();
        }finally{
            em.close();
        }
    }