Neos\Media\Controller\ThumbnailController::thumbnailAction PHP Method

    public function thumbnailAction(Thumbnail $thumbnail)
    {
        if ($thumbnail->getResource() === null && $thumbnail->getStaticResource() === null) {
            $this->thumbnailService->refreshThumbnail($thumbnail);
        }
        $this->redirectToUri($this->thumbnailService->getUriForThumbnail($thumbnail), 0, 302);
    }