Symfony 4 - Creation form - Object is null - symfony

Question

Symfony 4.3
Custom users provider (no FOS)
PHP 7.1 / MariaDB 10.2
Wamp local server
I already made users edit and users delete functions. It work PERFECT !
Now I want to create a registration form in my website but I don't understand the error !
Return value of App\Entity\User::getFirstname() must be of the type string, null returned
The exception :
in \src/Entity/User.php (line 100)
/**
* #ORM\Column(type="string")
* #Assert\NotBlank()
*/
private $firstname;
public function getFirstname(): string
{
return $this->firstname; // THIS IS LINE 100
}
Below is an extract from my UserController :
/**
* #Route("/users/add", name="app_users_add")
*/
public function addUser(Request $request, EntityManagerInterface $em): Response
{
$user = new User();
$form = $this->createForm(UserType::class, $user); // This line generates the error
[...]
return $this->render('user/add.html.twig', [
'form' => $form->createView()
]);
}
I really don't understand.
My UserEntity is working with my edit method in controller.
MY template user/add.html.twig is good (even if I let it empty)
My UserType form builder work well (I use the same for editing users)

Answer 1

you should add
public function getFirstname(): ?string
return $this->firstname;
}

Answer 2

The reason $form = $this->createForm(UserType::class, $user); generates an error is because you are passing $user as data to the form UserType. (this is refering to a file App\Form\UserType, right?). Since $user is a new object, $firstname of this user is not yet defined, thus the error occurs when you are passing the data of $user to the form. Simply removing the $user argument will work.
If you do not have a file App\Form\UserType, you can either create it or use createFormBuilder() in your controller. See the documentation for more information.