private void updateDownloadStatus(S3Object result) {
        if (result == null) {
            download.setState(Transfer.TransferState.Canceled);
            download.setMonitor(new DownloadMonitor(download, null));
        } else {
            download.setState(Transfer.TransferState.Completed);
        }
    }
Takes the result from serial download,
updates the transfer state and monitor in downloadImpl object
based on the result.
aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/transfer/internal/PresignUrlDownloadCallable.java