尝试将目录上载到S3(.NET API-C#)时出现NullReferenceException

浏览完网页后，我完全陷入了一个正在构建的应用程序中，该应用程序使用C#（Targeting.NET 4.5）将目录推送到Amazon S3。在使用TransferManager类的UploadDirectory（TransferUtilityUploadDirectoryRequest）方法推送目录文件的代码行中，我得到了NullReferenceException。问题是我找不到任何空的！调试器也没有显示任何null，所以我显然在这里缺少了一些东西。

我读到，如果你要上传到有句点的bucket，你需要将协议更改为HTTP，否则可能会引发NullReferenceException，但我也这样做了，并且继续收到错误，即使我创建了另一个没有句点的测试bucket。

我的代码直到&包括导致异常的行如下。名为S3Info的类只是我创建的一个助手类，它只存储一些配置信息，如访问/密钥和其他信息：

public static void uploadDirectories(S3Info info, List<DirectoryInfo> dirs, Logger logger = null)
    {
        AmazonS3Config alterConfig = new AmazonS3Config();
        alterConfig.CommunicationProtocol = Protocol.HTTP;
        AmazonS3Client s3Client = new AmazonS3Client(info.getCredentials(), alterConfig);
        TransferUtility directoryTransferUtil = new TransferUtility(s3Client);
        TransferUtilityUploadDirectoryRequest uploadDirRequest;
        PutObjectRequest completeFileUploadRequest;
        uint uploadSuccessCount = 0;
        if (dirs == null || dirs.Count == 0)
        {
            logger.log("Nothing to upload.");
            return;
        }
        //upload directory with PDFs
        foreach (DirectoryInfo dir in dirs)
        {
            try
            {
                //configure upload request
                uploadDirRequest = new TransferUtilityUploadDirectoryRequest();
                uploadDirRequest.BucketName = info.selectedBucket.BucketName;
                uploadDirRequest.Directory = dir.FullName;
                uploadDirRequest.KeyPrefix = dir.Name + @"'";
                uploadDirRequest.SearchOption = SearchOption.TopDirectoryOnly;
                uploadDirRequest.SearchPattern = "*.pdf";
                uploadDirRequest.Timeout = 600000; //10 minutes
                //upload directory!
                directoryTransferUtil.UploadDirectory(uploadDirRequest); //exception thrown here

我在这一点上有点停滞不前，所以我愿意接受社区提供的任何建议。谢谢

编辑：堆栈跟踪-

Object reference not set to an instance of an object. :    
at Amazon.S3.Transfer.Internal.UploadDirectoryCommand.Execute()
at Amazon.S3.Transfer.TransferUtility.UploadDirectory(TransferUtilityUploadDirectoryRequest request)
at S3Delivery.AmazonActions.uploadDirectories(S3Info info, List`1 dirs, Logger logger) in c:'Users'jblacker'Documents'Visual Studio 2012'Projects'S3Delivery'S3Delivery'AmazonActions.cs:line 173

第173行是上面提到的行。