code: func (e *Error) SetError(v interface{}) {
  	b, err := json.Marshal(v)
  	if err != nil {
  		panic("Error.SetData: " + err.Error())
  	}
  	e.Data = (*json.RawMessage)(&b)
  }
docs: // SetError sets e.Error to the JSON representation of v. If JSON
  // marshaling fails, it panics.