code: func GetNationalSignificantNumber(number *PhoneNumber) string {
  	// If leading zero(s) have been set, we prefix this now. Note this
  	// is not a national prefix.
  	nationalNumber := builder.NewBuilder(nil)
  	if number.GetItalianLeadingZero() {
  		zeros := make([]byte, number.GetNumberOfLeadingZeros())
  		for i := range zeros {
  			zeros[i] = '0'
  		}
  		nationalNumber.Write(zeros)
  	}
  	asStr := strconv.FormatUint(number.GetNationalNumber(), 10)
  	nationalNumber.WriteString(asStr)
  
  	return nationalNumber.String()
  }
docs: // Gets the national significant number of the a phone number. Note a
  // national significant number doesn't contain a national prefix or
  // any formatting.