code: func (ctx *ResCtx) ErrorData(v interface{}) error {
  	if ctx.Success {
  		return errors.New("ctx: cannot read error data since server returned a success response")
  	}
  	if ctx.errorData == nil {
  		return errors.New("ctx: server did not return any error data")
  	}
  
  	if err := json.Unmarshal(ctx.errorData, v); err != nil {
  		return fmt.Errorf("ctx: cannot deserialize error data: %v", err)
  	}
  	return nil
  }
docs: // ErrorData reads the error response data into given object.
  // Object should be passed by reference.