How to set json value?

Question

symfony

/**
 * @ORM\Entity(repositoryClass=DeliveryRepository::class)
 */
class Delivery {
/**
     * @ORM\Id
     * @ORM\GeneratedValue
     * @ORM\Column(type="integer")
     */
    private $id;
    /**
     * @ORM\Column(type="json", nullable=true)
     */
    private json = [];
public function getJson()
    {
        return $this->json;
    }

    public function setJson($json): self
    {
        $this->json = $json;

        return $this;
    }

}

$d=new Delivery();
$d->setJson(["fff"=>["ff"=>[1,3]],"hh3"=>[7,8]]); // пробовала 1
$d->setJson(["fff"]); // пробовала 2

does not save throws an error

Call to a member function setJson() on array

googled, didn't find anything...