我想用下面的方法删除30天的旧blobs。不过，好像“sourceBlob.getProperties()的部分。getLastModified()。getTime()；"生成异常。可能的解决方案是什么？异常消息仅显示null。Azure存储类型是存储(通用v1)

public static void deleteOldBlobs(String source) {
    try {
        System.out.println("deleteOldBlobs started");
        CloudStorageAccount storageAccount = CloudStorageAccount
                .parse(PropertyUtil.getProperty("storageConnectionString"));
        CloudBlobClient blobClient = storageAccount.createCloudBlobClient();
        CloudBlobContainer sourceContainer = blobClient.getContainerReference(source);
        long daysBack = 30;
        System.out.println(daysBack);
        long cutoff = (daysBack * (24 * 60 * 60 * 1000));
        for (ListBlobItem blobItem : sourceContainer.listBlobs()) {
            String sourceFileName = new File(blobItem.getUri().toString()).getName();
            System.out.println(sourceFileName);
            CloudBlockBlob sourceBlob = sourceContainer.getBlockBlobReference(sourceFileName);
            System.out.println(sourceBlob.getProperties().getLastModified().getTime());
            long diff = new Date().getTime()- sourceBlob.getProperties().getLastModified().getTime();

            if (diff > cutoff) {
                sourceBlob.deleteIfExists();
            }
        }
        System.out.println("deleteOldBlobs ended");
    } catch (Exception ex) {
        System.out.println(ex.getMessage());
    } finally {
    }
}