how to handle adding null values with eachother - flutter

Question

I want to input three numbers into TextFormFields. The controllers are numOneController and numTwoController for putting the percent and a totalAmountController for putting the the amount. I then want to check if the percents are in total 100 so i can display they are indeed so. When totalAmountController is empty(null) then its no problem to display that its an invalid input but when the numOneController and numTwoController are empty i get the error Invalid number (at character 1). I know its the fact that handler can't add an empty number with another. But how can i handle this so i can check if its null then i want to assign a number 0 to add that automaticly.
sumHandler() {
var totalPrecent = int.parse(numOneController.text) +
int.parse(numTwoController.text) ;
var totalAmount = totalAmountController;
if (totalPrecent == 100 && totalAmount.text.isEmpty == false) {
debugPrint(totalPrecent.toString());
debugPrint(totalAmount.text.toString());
} else {
debugPrint("invalid input");
}
}

Answer 1

Using the tryParse method and a default value would help...
sumHandler() {
var totalPrecent = int.tryParse(numOneController.text) ?? 0 +
int.tryParse(numTwoController.text) ?? 0;
var totalAmount = totalAmountController;
if (totalPrecent == 100 && totalAmount.text.isEmpty == false) {
debugPrint(totalPrecent.toString());
debugPrint(totalAmount.text.toString());
} else {
debugPrint("invalid input");
}
}

Answer 2

So i found the solution for this on: Another exception was thrown: FormatException: Invalid number (at character 1)
I had to use try catch block:
try {
firstNumber = int.parse(numOneController.text);
} on FormatException {
firstNumber = 0;
}
This way i can handle the exception and on FormatException i can assign the number 0.

Answer 3

Create a temp variable and store it with 0 and later if the textfield has values assign values to it. Like the following
sumHandler() {
int firstNumber = 0;
int secondNumber = 0;
if(numOneController.text != "")
{
firstNumber = int.parse(numOneController.text);
}
if(numTwoController.text != "")
{
secondNumber = int.parse(numTwoController.text);
}
var totalPresent = firstNumber + secondNumber ;
var totalAmount = totalAmountController;
if (totalPresent == 100 && totalAmount.text.isEmpty == false) {
debugPrint(totalPresent.toString());
debugPrint(totalAmount.text.toString());
} else {
debugPrint("invalid input");
}
}