code: func toStatus(err error) error {
  	switch {
  	case err == mapper.ErrNoSuchJob:
  		return status.Errorf(codes.NotFound, "no such mapping job")
  	case transient.Tag.In(err):
  		return status.Errorf(codes.Internal, err.Error())
  	case err != nil:
  		return status.Errorf(codes.InvalidArgument, err.Error())
  	default:
  		return nil
  	}
  }
docs: // toStatus converts an error from mapper.Controller to an grpc status.
  //
  // Passes nil as is.