isVatRateValid function
Implementation
bool isVatRateValid(MatexVatCalculatorState state) {
return (state.vatRate != null && state.vatRate! > 0 && state.vatRate! < 1) ||
(state.federalVatRate != null &&
state.federalVatRate! > 0 &&
state.federalVatRate! < 1) ||
(state.regionalVatRate != null &&
state.regionalVatRate! > 0 &&
state.regionalVatRate! < 1);
}