jpush php ios推送平台推送有消息和声音，但是代码推送没有声音

代码是这样的
public function addIosNotification($alert=null, $sound=null, $badge=null, $content_available=null, $category=null, $extras=null) {
$ios = array();

    if (!is_null($alert)) {
        if (!is_string($alert) && !is_array($alert)) {
            throw new InvalidArgumentException("Invalid ios alert value");
        }
        $ios['alert'] = $alert;
    }

    if (!is_null($sound)) {
        if (!is_string($sound)) {
            throw new InvalidArgumentException("Invalid ios sound value");
        }
        if ($sound !== JPush::DISABLE_SOUND) {
            $ios['sound'] = $sound;
        }
    } else {
        // 默认sound为''
        $ios['sound'] = 'sound.caf';
    }