Nextras\MailPanel\SessionMailer::requireSessions PHP Method

    private function requireSessions()
    {
        if (!$this->session->isStarted()) {
            throw new \RuntimeException('Session is not started, start session or use FileMailer instead.');
        }
        if (!isset($this->sessionSection->messages)) {
            $this->sessionSection->messages = array();
        }
    }