public function getAction(Exercise $exercise, Paper $paper, User $user)
    {
        $this->assertHasPermission('OPEN', $exercise);

        if (!$this->isAdmin($paper->getExercise()) && $paper->getUser() !== $user) {
            // Only administrator or the User attached can see a Paper
            throw new AccessDeniedException();
        }

        return new JsonResponse($this->paperManager->serialize($paper));
    }