Symfony 4.x ROLE_USER error when rendering a form with $form->createView() - symfony-4.2

Question

I'm creating a blog with Symfony 4 and generate forms with :
php bin/console make:form
when I try to render it like this :
/**
* Require ROLE_USER for only this controller method.
* #Route("/create", name="post.create")
* #return Response
*/
public function create(): Response
{
$post = new Post();
$form = $this->createForm(CreatePostType::class, $post);
return new Response($this->twig->render('pages/create.html.twig'), [
'form' => $form->createView()
]);
}
I get this error
Could not convert database value "'ROLE_USER'" to Doctrine Type json
for this line
'form' => $form->createView()
Here is my getRoles :
/**
* #see UserInterface
*/
public function getRoles(): array
{
$roles = $this->roles;
// guarantee every user at least has ROLE_USER
$roles[] = 'ROLE_USER';
return array_unique($roles);
}
and my security.yaml
security:
# https://symfony.com/doc/current/security.html#where-do-users-come-from-user-providers
providers:
in_memory: { memory: ~ }
firewalls:
dev:
pattern: ^/(_(profiler|wdt)|css|images|js)/
security: false
main:
anonymous: ~
I'm searching for 3 days and restarted my project in a 2nd directory without the security management, I don't understand were it's from and how to solve it
thanks

Answer 1

I guess the roles property is not stored as json-type in your database. Can you check the type of the roles field in the database?
As a sidenote, you can rewrite the response to:
return $this->render('pages/create.html.twig', [
'form' => $form->createView(),
]);