def METHOD_NAME(self, id=None):
    """ Retrive the model bundle from a combiner. """
    channel = Channel(self.address, self.port,
                      self.certificate).get_channel()
    modelservice = rpc.ModelServiceStub(channel)
    if not id:
        id = self.get_model_id()
    data = BytesIO()
    data.seek(0, 0)
    parts = modelservice.Download(fedn.ModelRequest(id=id))
    for part in parts:
        if part.status == fedn.ModelStatus.IN_PROGRESS:
            data.write(part.data)
        if part.status == fedn.ModelStatus.OK:
            return data
        if part.status == fedn.ModelStatus.FAILED:
            return None