App\Entity\User.php

<?php

// ...

class User implements UserInterface
{

    /**
     * ...
     * @Assert\NotBlank()
     * @Assert\Length(max="255")
     */
    public $name;

    /**
     * ...
     * @Assert\NotBlank()
     * @Assert\Length(max="255")
     */
    public $email;

    /**
     * ...
     * @Assert\NotBlank()
     * @Assert\Length(max="255")
     */
    public $plainPassword;

    // ...
}