Symfony error : EntityManager#remove() expects parameter 1 to be an entity object, NULL given

I’m new to symfony, I’m trying to build a little web projet and I met an error on my symfony
interface.

I get this error while I want laugh my web project :

EntityManager#remove() expects parameter 1 to be an entity object, NULL given.

And here is the related code :

    public function homepage(EntityManagerInterface $em)
    {

        $productRepository = $em->getRepository(Product::class);

        $product = $productRepository->find(3);


            $em->remove($product);

            $em->flush();


        dd($product);

        return $this->render('home.html.twig');
    }

}

Someone can help me to fix it ?

I tried to change the value setting of the $product but nothing happens.