code: func (ctx *BatchedContext) errors() error {
  	if !ctx.checkResults() {
  		return nil
  	}
  	err := make(errorSlice, len(ctx.results))
  	for i, res := range ctx.results {
  		err[i] = result(res)
  	}
  	return err
  }
docs: // errors convert ctx.results into errors