The setter 'setValue=' was called on null - flutter

Question

I am trying to assign an input value into my model in order to use it in the API POST request. However, I keep getting the error:
setter was called on null when saving
Model:
#JsonSerializable()
class Discount {
String value;
Discount();
set setValue(String value) {
this.value = value;
}
Dart Code:
children: <Widget>[
Expanded(
child: Container(
margin: EdgeInsets.only(right: 5),
child: TextFormField(
initialValue: _invoiceFormData.discount?.value ?? '0.00',
inputFormatters: [_amountValidator],
keyboardType: TextInputType.numberWithOptions(
decimal: true,
signed: false,
),
decoration: TextFormField.decoration(
labelText: Localizations.of(context)
.text('label_invoice_discount'),
),
onChanged: (String value) {
setState(() {
discountTotal = value;
});
},
onSaved: (value) => _invoiceFormData
.discount.setValue = value,
),
),
),
FlatButton(
onPressed: () {
setState(() {
discountType = !discountType;
});
},
),
],
Log:
The setter 'setValue=' was called on null.
Receiver: null
Tried calling: setValue="10.00"
I tried to set _invoiceFormData.discount.value = value but it is still showing the same error.

Answer 1

use StatefulWidget class and
change this
onSaved: (value) => _invoiceFormData
.discount.setValue = value,
to
onSaved: (value) => setState(() {
onSaved: (value) => _invoiceFormData
.discount.setValue = value,
});

Answer 2

Your log is saying that _invoiceFormData.discount is null when you are using the setter setValue=.
To resolve this, you first need to instantiate the field discount in your object named _invoiceFormData. For example, when you initialize this form data (maybe in your initState()), you should do _invoiceFormData.discount = Discount(); then it will not be null anymore