Symfony 4 Notice: Trying to access array offset on value of type null

I got a project on Symfony 4, since i install that project on my new computer with the latest version of PHP 7.4, i have an error on some query but not in all my controller.

Heres the method in the controller

/** * @Route("/juge/{userId}/jugementCategorie/{id}", name="jugementCategorie") */public function jugementCategorie($id, $userId, CategorieRepository $repoCat, ResultatRepository $repoResult, KaratekaRepository $repoKarateka){    $actif = [];    $categorie = $repoCat->find($id);    $karatekas = $categorie->getKarateka();    $resultats = $repoResult->findResultatCategorieJuge($id, $userId);    $activeKarateka = $repoKarateka->findByActiveInCat($id);    if(isset($activeKarateka)){        $count = 0;        foreach($activeKarateka->getResultats() as $resultat){            if($resultat->getUser()->getId() == $userId && $resultat->getCategorie()->getId() == $id){                $count++;                               }                }        if($count == 0){            $actif = $activeKarateka;        }    }    return $this->render('juge/jugementCategorie.html.twig', ['categorieId' => $id,'actif' => $actif,'resultats' => $resultats,    ]);}

When i try to access this page i have this error

I got some ajax call that are not working when calling methods in that specific controller too.

I'm really confuse, anybody have a hint for me?

Thanks for your help