Problems accessing metadata

Question

I am trying to get a particular metadata property from a file into Bridge JavaScript. I can see many metadata properties in JavaScript and the one I want is listed in the metadata panel in Bridge, but I can't see to figure out how to access it programmatically.
The one I'm interested in is the RAW filename. It's my understanding that this code should work for accessing it, but it doesn't.
var metaData = thumb.metadata;
metaData.namespace = "http://ns.adobe.com/camera-raw-settings/1.0/";
var acrRawFileName = metaData.RawFileName;
But, even though I can see this property in Bridge, all I get in JavaScript is an empty string. I can access other properties in other namespaces like DateTimeOriginal in the EXIF namespace.
Anyone know how to programmatically access the original raw filename in the camera raw metadata namespace?
--John

Answer 1

It's my mistake. It appears that that property is only populated "after" ACR saves a change to the file, so it's only on some of my RAW files. For the ones where it is present, the previous code works.
I was trying to use this propery as a "master file ID" so I can track subsequent derivative versions because this property is present in PSDs or JPEGs derived from this RAW file. I think I can just add some logic that if this field is empty and the filetype is RAW, then just use the filename itself as the master file ID. Thanks.
--John