Flutter: showDialog: build function returned null - dart

Question

I have a StatefulWidget. Then when I click a button, it shows an alert dialog. When I implement:
onTap: () {
showDialog(
context: context,
builder: (BuildContext context) {
return AlertDialog(
title: Text("Hello"),
);
}
}
Everything works fine. But when I transfered the things inside the builder to a different StatefulWidget, then this error occurs:
A build function returned null.
I/flutter ( 3647): The offending widget is: Builder
I/flutter ( 3647): Build functions must never return null. To return an empty space that causes the building widget to
I/flutter ( 3647): fill available room, return "new Container()". To return an empty space that takes as little room as
I/flutter ( 3647): possible, return "new Container(width: 0.0, height: 0.0)".
Here is the code:
Here is the calling StatefulWidget:
onTap: () {
showDialog(
context: context,
builder: (BuildContext context) {
LastVacDialog(
currentDose: currDose,
currentDate: currDate,
currentIndex: i,
setValue: changeDoseValueAndDate,
);
},
);
},
Here is the new StatefulWidget:
class LastVacDialog extends StatefulWidget {
LastVacDialog({
this.currentDose,
this.currentDate,
this.setValue,
this.currentIndex,
});
final int currentDose;
final DateTime currentDate;
final void Function(int, DateTime, int) setValue;
final currentIndex;
#override
LastVacDialogState createState() => new LastVacDialogState();
}
class LastVacDialogState extends State<LastVacDialog> {
int _dose;
DateTime _today;
#override
Widget build(BuildContext context) {
return AlertDialog(
title: Text("Last Dose"),
);
}
}
Is there something wrong with my code? I just omitted some variables for simplicity.

Answer 1

Add the Word Return in Front of - LastVacDialog
builder: (BuildContext context) {
return LastVacDialog(
...
As Error is Stating Build function must never return null. So return your LastVacDialog Widget by adding return in front of it.