title: A value of type 'Null' can't be assigned to a parameter of type 'String' in a const constructor
body: <p>I'm unable to use <code>questions[questionNumber]</code> as a Text Constructor in Flutter.</p>
  <p><strong>Errors:</strong></p>
  <p>Evaluation of this constant expression throws an exception.dart(const_eval_throws_exception)</p>
  <p>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</p>
  <p>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</p>
  <pre><code>class _QuizPageState extends State&lt;QuizPage&gt; {
    List&lt;Widget&gt; scoreKeeper = [];
    List&lt;String&gt; 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,
                  ),
                ),
              ),
            ),
          ),
       ],
      );
    }
  }
  </code></pre>