code: func Code(err error) codes.Code {
  	if code, ok := Tag.In(err); ok {
  		return code
  	}
  	// TODO(nodir): use status.FromError
  	return grpc.Code(errors.Unwrap(err))
  }
docs: // Code returns the gRPC code for a given error.
  //
  // In addition to the functionality of grpc.Code, this will unwrap any wrapped
  // errors before asking for its code.