code: func registerBarcode(pdf barcodePdf, bcode barcode.Barcode, err error) string {
  	if err != nil {
  		pdf.SetError(err)
  		return ""
  	}
  
  	return Register(bcode)
  }
docs: // registerBarcode registers a barcode internally using the Register() function.
  // In case of an error generating the barcode it will not be registered and will
  // set an error on the PDF. It will return a unique key for the barcode type and
  // content that can be used to put the barcode on the page.