code: func (r Registry) Unregister(name string) error {
  	if _, ok := r[name]; !ok {
  		return fmt.Errorf("no plugin named %v exists", name)
  	}
  	delete(r, name)
  	return nil
  }
docs: // Unregister removes an existing plugin from the registry. If no plugin with
  // the provided name exists, it returns an error.