Different ways to show or not show null Strings in Text Widgets in Flutter

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  String? firtstNullText, secondNullText, thirdNullText;
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(),
        floatingActionButton: FloatingActionButton(
            onPressed: () {
              setState(() {
                firtstNullText = 'now first text is not null';
                secondNullText = 'now second text is not null';
                thirdNullText = 'now third text is not null';
              });
            },
            child: const Text('Put Text', textAlign: TextAlign.center)),
        body: Center(
          child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                //'Firt Example
                //Here if you delete the space after the ??, you can't see the red container
                Container(color:Colors.red, child: Text(firtstNullText ?? ' '),),
                //Second Example
                if (secondNullText != null) Container(color:Colors.blue, child: Text(secondNullText!)),
                //Third Example
                //The only one you can see before you press the fab button in the bottomRight corner, show 'null' word.
                Container(color:Colors.green, child: Text('$thirdNullText')),
              ]),
        ),
      ),
    );
  }
}