JSON Serialization of empty objects fails

Passing valid json, like this will fail in FileTransfer.upload
{
"filePath": "/CapturedImagesCache/CameraCapture-930aa659-6057-4c57-89f0-1f53b238da70.jpg",
"server": "http://myserverdotcom",
"fileKey": "file",
"fileName": "CameraCapture-930aa659-6057-4c57-89f0-1f53b238da70.jpg",
"mimeType": "image/jpeg",
"params": {}
}