JsonResponse Não retorna os dados

Estou realizando o select dos dados da classe que criei porém não esta retornando em Json

 <?php

namespace App\Controller;

use App\Entity\Marca;
use App\Helper\MarcaFactory;
use Doctrine\ORM\EntityManagerInterface;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\JsonResponse;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Routing\Annotation\Route;
use Symfony\Component\Validator\Constraints\Collection;


class MarcaController extends AbstractController
{
    /**
     * @var EntityManagerInterface
     */
    private $entityManager;
    /**
     * @var MarcaFactory
     */
    private $marcaFactory;

    public function __construct(
        EntityManagerInterface $entityManager,
        MarcaFactory $marcaFactory)
    {
        $this->entityManager = $entityManager;
        $this->marcaFactory  = $marcaFactory;
    }

    /**
     * @Route("/marca", methods={"POST"})
     */
    public function salvar(Request $request): Response
    {
        $corpoRequisicao = $request->getContent();
        $dadosEmJson = json_decode($corpoRequisicao);

        $marca = new Marca();

        $marca->setMarca($dadosEmJson->marca);

        $this->entityManager->persist($marca);

        $this->entityManager->flush();

        return new JsonResponse($marca);
    }

    /**
     * @Route("/marca", methods={"GET"})
     */
    public function listar(): Response
    {
        //return new JsonResponse($this->repository->findAll());
        $repositorioDeMarcas = $this
            ->getDoctrine()
            ->getRepository(Marca::class);

        $marcaList = $repositorioDeMarcas->findAll();
        foreach ($marcaList as $marca){
            echo($marca->getMarca() . "\n");
        }

        return new JsonResponse($marcaList);
    }
}

O retorno gerado no browser sai assim:

Coca-Cola Skol Aee Aee Aee [{},{},{},{},{}]

Com echo sai ok, por meio do JsonResponse vazio.