无法在collectionView Swift 4

Question

这是我的代码的一部分（用Swift 4编写，xcode 9.2），我想这样做。

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "customCell", for: indexPath) as! CustomCollectionViewCell
if let thumbnailImage = getThumbnailImage(forUrl: str!) {
        cell.imageView.image = thumbnailImage
    }
    cell.nameLabel.text = devices[indexPath.row].name.capitalized
    print(devices[indexPath.row].url)
    return cell
}

和getThumnailImage函数

func getThumbnailImage(forUrl url: URL) -> UIImage? {
    let asset: AVAsset = AVAsset(url: url)
    let imageGenerator = AVAssetImageGenerator(asset: asset)
    do {
        let thumbnailImage = try imageGenerator.copyCGImage(at: CMTimeMake(1, 60) , actualTime: nil)
        return UIImage(cgImage: thumbnailImage)
    } catch let error {
        print(error)
    }
    return nil
}

当我运行它时，我收到此错误：

  

错误域= AVFoundationErrorDomain代码= -11850“操作已停止”UserInfo = {NSLocalizedFailureReason =服务器未正确配置。，NSLocalizedDescription =操作已停止，NSUnderlyingError = 0x61c00044fbd0 {错误域= NSOSStatusErrorDomain代码= -12939“（null）” }}