code: func WrapIfTransient(err error) error {
  	if err == nil {
  		return nil
  	}
  
  	if IsTransientCode(Code(err)) {
  		err = transient.Tag.Apply(err)
  	}
  	return err
  }
docs: // WrapIfTransient wraps the supplied gRPC error with a transient wrapper if
  // it has a transient gRPC code, as determined by IsTransientCode.
  //
  // If the supplied error is nil, nil will be returned.
  //
  // Note that non-gRPC errors will have code grpc.Unknown, which is considered
  // transient, and be wrapped. This function should only be used on gRPC errors.