public function convertToRegistered($sendNotification = true)
    {
        // Already a registered user
        if (!$this->is_guest) {
            return;
        }

        if ($sendNotification) {
            $this->generatePassword();
        }

        $this->is_guest = false;
        $this->save();

        if ($sendNotification) {
            $this->sendInvitation();
        }
    }