File upload 错误的JSON:预期的对象值。Dropbox API文件上载错误

我正在尝试使用Dropbox java sdk将文件上载到Dropbox

我在dropbox中创建了一个应用程序，授予了写入权限，应用程序状态为开发

代码一直工作到“写入模式完成”记录器，然后失败fileStream属于InputStream类型

DbxClientV2 client = createClient();
    String path = "/" + fileName.toString();
    try {
        System.out.println("STARTING...............");
        UploadBuilder ub = client.files().uploadBuilder(path);
        System.out.println("ub done");
        ub.withMode(WriteMode.ADD);
        System.out.println("write mode done");
        FileMetadata metadata = ub.uploadAndFinish(fileStream);
        System.out.println("File uploaded");
        System.out.println(metadata.toStringMultiline());
        ;
        System.out.println("FINISHED...............");
    } catch (IOException e) {
        e.printStackTrace();
    }

我得到的例外是

com.dropbox.core.BadResponseException: Bad JSON: expected object value.
at [Source: ; line: 1, column: 1]
at com.dropbox.core.DbxRequestUtil.unexpectedStatus(DbxRequestUtil.java:347)
at com.dropbox.core.DbxRequestUtil.unexpectedStatus(DbxRequestUtil.java:324)
at com.dropbox.core.DbxUploader.finish(DbxUploader.java:268)
at com.dropbox.core.DbxUploader.uploadAndFinish(DbxUploader.java:126)
.
.
.
Caused by: com.fasterxml.jackson.core.JsonParseException: expected object value.
at [Source: ; line: 1, column: 1]
at com.dropbox.core.stone.StoneSerializer.expectStartObject(StoneSerializer.java:91)
at com.dropbox.core.ApiErrorResponse$Serializer.deserialize(ApiErrorResponse.java:53)

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[交叉链接以供参考：]呼叫返回401状态代码。重新生成访问令牌解决了该问题。