Filter by KeyProperty in Google datastore with Dart

I try to run a query which filters for a KeyProperty. The dart gcloud package I am currently using is version: 0.2.0+8

So for a Model like this:

@Kind(idType: IdType.String)
class Foo extends Model {
  @ModelKeyProperty(indexed: true, required: true)
  Key bar;
}

I would like to run a query like so:

Query query = new Query(db, Foo);
query.filter('bar =', someKey);
var result = query.run();

but I receive following error:

Uncaught error in request handler: ApplicationError: Cannot encode unsupported Key type.
#0      Codec.encodeProperty (package:appengine/src/api_impl/raw_datastore_v3_impl.dart:319:7)
#1      DatastoreV3RpcImpl.query (package:appengine/src/api_impl/raw_datastore_v3_impl.dart:527:43)
#2      Query.run.<anonymous closure> (package:gcloud/src/db/db.dart:232:28)

Assuming

import 'package:gcloud/datastore.dart' as datastore;
import 'package:gcloud/db.dart';

In my previous experiments, I remember having to convert the Key (from db.dart) to a datastore.Key. I don't know why this API expects this while the others handle db.Key correctly so I cannot tell whether it is a bug or not but the following should work:

await db.withTransaction((Transaction transaction) async {
  // convert the key to a datastore key
  datastore.Key datastoreKey = db.modelDB.toDatastoreKey(someKey);

  // query by bar key
  Query query = transaction.query(Foo, ancestorKey);
  query.filter('bar =', datastoreKey);
  await query.run().listen((Model model) {
    print(model.key.id);
  }).asFuture();
});