On lines 13-16. is that not correct?

namespace App\Entity;

use App\Repository\ConferenceRepository;
use Doctrine\ORM\Mapping as ORM;

#[ORM\Entity(repositoryClass: ConferenceRepository::class)]
class Conference
{
    #[ORM\Column(type: 'integer')]
    #[ORM\Id, ORM\GeneratedValue()]
    private $id;

    #[ORM\Column(type: 'string', length: 255)]
    private $city;

    // ...

    public function getCity(): ?string
    {
        return $this->city;
    }

    public function setCity(string $city): self
    {
        $this->city = $city;

        return $this;
    }

    // ...
}