Symfony 4 - repository problem

doctrine.yml

parameters:
    # Adds a fallback DATABASE_URL if the env var is not set.
    # This allows you to run cache:warmup even if your
    # environment variables are not available yet.
    # You should not need to change this value.
    env(DATABASE_URL): ''

doctrine:
    dbal:
        # configure these for your database server
        driver: 'pdo_mysql'
        server_version: '5.7'
        charset: utf8mb4

        # With Symfony 3.3, remove the `resolve:` prefix
        url: '%env(resolve:DATABASE_URL)%'
    orm:
        auto_generate_proxy_classes: '%kernel.debug%'
        naming_strategy: doctrine.orm.naming_strategy.underscore
        auto_mapping: true
        mappings:
            App:
                is_bundle: false
                type: annotation
                dir: '%kernel.project_dir%/src/Entity'
                prefix: 'App\Entity'
                alias: App

Produto.php

<?php

namespace App\Entity;

use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\Validator\Constraints as Assert;

/**
 * @ORM\Entity(repositoryClass="App\Repository\ProdutoRepository")
 */
class Produto
{
    /**
     * @ORM\Id
     * @ORM\GeneratedValue
     * @ORM\Column(type="integer")
     */
    private $id;

    /**
     * @ORM\Column(type="string", length=100)
     * @Assert\NotBlank()
     */
    private $nome;

    /**
     * @ORM\Column(type="decimal", scale=2)
     * @Assert\NotBlank()
     */
    private $preco;

    /**
     * @ORM\Column(type="text")
     * @Assert\NotBlank()
     */
    private $descricao;

    /**
     * @return mixed
     */
    public function getId()
    {
        return $this->id;
    }

    /**
     * @return mixed
     */
    public function getNome()
    {
        return $this->nome;
    }

    /**
     * @param mixed $nome
     *
     * @return Produto
     */
    public function setNome($nome)
    {
        $this->nome = $nome;

        return $this;
    }

    /**
     * @return mixed
     */
    public function getPreco()
    {
        return $this->preco;
    }

    /**
     * @param mixed $preco
     *
     * @return Produto
     */
    public function setPreco($preco)
    {
        $this->preco = $preco;

        return $this;
    }

    /**
     * @return mixed
     */
    public function getDescricao()
    {
        return $this->descricao;
    }

    /**
     * @param mixed $descricao
     *
     * @return Produto
     */
    public function setDescricao($descricao)
    {
        $this->descricao = $descricao;

        return $this;
    }
}

ProdutoController.php

<?php

namespace App\Controller;

use App\Repository\ProdutoRepository;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;

class ProdutoController extends Controller
{
    /**
     * @Route("/produto", name="produto")
     */
    public function index()
    {
        $em = $this
            ->getDoctrine()
            ->getManager();

        $produtos = $em->getRepository(ProdutoRepository::class)->findAll();

        return $this->render("produtos/index.html.twig", ['produtos' => $produtos]);
    }    
}

ProdutoRepository.php

<?php

namespace App\Repository;

use App\Entity\Produto;
use Doctrine\Bundle\DoctrineBundle\Repository\ServiceEntityRepository;
use Symfony\Bridge\Doctrine\RegistryInterface;

class ProdutoRepository extends ServiceEntityRepository
{
    public function __construct(RegistryInterface $registry)
    {
        parent::__construct($registry, Produto::class);
    }

    /*
    public function findBySomething($value)
    {
        return $this->createQueryBuilder('p')
            ->where('p.something = :value')->setParameter('value', $value)
            ->orderBy('p.id', 'ASC')
            ->setMaxResults(10)
            ->getQuery()
            ->getResult()
        ;
    }
    */
}