OCA\Richdocuments\Controller\SessionController::validateSession PHP Method

    protected function validateSession($session)
    {
        try {
            if (is_null($this->shareToken)) {
                new File($session->getFileId());
            } else {
                File::getByShareToken($this->shareToken);
            }
        } catch (\Exception $e) {
            $this->logger->warning('Error. Session no longer exists. ' . $e->getMessage(), ['app' => $this->appName]);
            $ex = new BadRequestException();
            $ex->setBody(implode(',', $this->request->getParams()));
            throw $ex;
        }
    }