Неправильный размер вложения в msgraph api

Размер свойства FileAttachment больше, чем фактический размер двоичного файла.

 {
    "@odata.type": "#microsoft.graph.fileAttachment",
    "@odata.mediaContentType": "application/octet-stream",
    "id": "<the attachment id>",
    "lastModifiedDateTime": "2020-10-26T09:57:36Z",
    "name": "test.bin",
    "contentType": "application/octet-stream",
    "size": 245,
    "isInline": false,
    "contentId": null,
    "contentLocation": null,
    "contentBytes": "aGVsbG8gd29ybGQ="
}

Вот фрагмент кода java, созданный над данными json:

IGraphServiceClient graphClient = GraphServiceClient.builder().authenticationProvider(provider).buildClient();
FileAttachment attachment = new FileAttachment();
attachment.oDataType = "#microsoft.graph.fileAttachment";
attachment.name = "test.bin";
attachment.contentBytes = "hello world".getBytes();

Attachment att = graphClient.users().byId(userId).messages().byId(mailId).attachments().buildRequest().post(attachment);
System.out.println(att.size);