private function sessions() : array
    {
        if (!empty($sessions)) return $sessions;

        $returnSessions = [];

        $sessions = $this->get(sprintf(Session::SESSION_ENDPOINT, $this->onlineIdParameter), [
            'fields' => '@default,npTitleDetail,npTitleDetail.platform,sessionName,sessionCreateTimestamp,availablePlatforms,members,memberCount,sessionMaxUser',
            'titleIconSize' => 's',
            'npLanguage' => 'en'
        ]);

        if ($sessions->size === 0) return null;

        // Multiple sessions could be used if the user is in a party while playing a game.
        foreach ($sessions->sessions as $session) {
            $returnSessions[] = new Session($this->client, $session);
        }

        $sessions = $returnSessions;

        return $returnSessions;
    }