code: func IsNotImplementedError(err error) bool {
  	if e, ok := err.(interface {
  		NotImplemented() bool
  	}); ok {
  		return e.NotImplemented()
  	}
  	if parent := parentOf(err); parent != nil {
  		return IsNotImplementedError(parent)
  	}
  	return false
  }
docs: // IsNotImplementedError indicates the client attempted to use a feature the
  // server has not implemented (e.g. the batch endpoint).