MPMediaPickerController-> MPmediaitem -> NSDATA (xamarin, c#, ios)

Question

async void SoundPickingMedia(object sender, ItemsPickedEventArgs args)
{
    if (args.MediaItemCollection.Items != null)
    {
        foreach (var item in args.MediaItemCollection.Items)
        {
            NSError error;
            NSUrl url = item.AssetURL;
            NSData data = NSData.FromUrl(url, 0, out error);
            Stream stream = data.AsStream();
         }
    }
}

NSUrl url -> null

how to use AVAssetExportSession from xamarin c#?