A value of type 'Null' can't be assigned to a parameter of type 'String' in a const constructor

I'm unable to use ```questions[questionNumber]``` as a Text Constructor in Flutter.

**Errors:**

Evaluation of this constant expression throws an exception.dart(const_eval_throws_exception)

A value of type 'Null' can't be assigned to a parameter of type 'String' in a const constructor.
Try using a subtype, or removing the keyword 'const'.dartconst_constructor_param_type_mismatch

Arguments of a constant creation must be constant expressions.
Try making the argument a valid constant, or use 'new' to call the constructor.dartconst_with_non_constant_argument

```
class _QuizPageState extends State<QuizPage> {
List<Widget> scoreKeeper = [];
List<String> questions = [
'You can lead a cow down stairs but not up stairs.',
'Approximately one quarter of human bones are in the feet.',
'A slug\'s blood is green.'
];

int questionNumber = 0;

@override
Widget build(BuildContext context) {
return Column(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: [
const Expanded(
flex: 5,
child: Padding(
padding: EdgeInsets.all(10.0),
child: Center(
child: Text(
questions[questionNumber],
textAlign: TextAlign.center,
style: TextStyle(
fontSize: 25.0,
color: Colors.white,
),
),
),
),
),
],
);
}
}
```

Well, the error is due to using the keyword `const` for the `Expanded` widget. Just remove it and you will be all good.

So this:
```
@override
Widget build(BuildContext context) {
return Column(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: [
Expanded(
flex: 5,
child: Padding(
padding: EdgeInsets.all(10.0),
child: Center(
child: Text(
questions[questionNumber],
textAlign: TextAlign.center,
style: TextStyle(
fontSize: 25.0,
color: Colors.white,
),
),
),
),
),
],
);
}
}
```

remove keyword `const` before the Expanded widget.


class _QuizPageState extends State<QuizPage> {
List<Widget> scoreKeeper = [];
List<String> questions = [
'You can lead a cow down stairs but not up stairs.',
'Approximately one quarter of human bones are in the feet.',
'A slug\'s blood is green.'
];

int questionNumber = 0;

@override
Widget build(BuildContext context) {
return Column(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: [
Expanded(
flex: 5,
child: Padding(
padding: EdgeInsets.all(10.0),
child: Center(
child: Text(
questions[questionNumber],
textAlign: TextAlign.center,
style: TextStyle(
fontSize: 25.0,
color: Colors.white,
),
),
),
),
),
],
);
}
}