Google Fit DataSource Device (device that collects data) is null

I'm using the Google Fit API on an Android phone. Subscribing to various data types and pulling the data from history works fine. I'm trying to get information about the device that recorded the data, i.e. the phone. According to the documentation, the DataSource has a getDevice() method, that returns "the device where data is being collected" - but the device is null. Why?

My code to access the device information:

 val request = DataReadRequest.Builder()
                .setTimeRange(from, to, TimeUnit.MILLISECONDS)
                .enableServerQueries()
                .setLimit(DATA_POINT_LIMIT)

 request.read(DataType.TYPE_ACTIVITY_SEGMENT)

 historyClient.readData(request.build())
     .addOnSuccessListener {
         data.dataSets.forEach {
             //it.dataSource //Data source is not null
             //it.dataSource.device //Device is null
         }
 }

https://developers.google.com/android/reference/com/google/android/gms/fitness/data/DataSource#getDevice()

The DataSource you get back corresponds to the merged DataSource for that DataType; it'll contain DataPoints for various origin DataSources.

For a given DataPoint you can retrieve the origin DataSource using this method (subject to the caveats in the documentation): https://developers.google.com/android/reference/com/google/android/gms/fitness/data/DataPoint#getOriginalDataSource()