Optional Widgets with nullable parameter

main.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Optional Widgets with nullable parameter',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Optional Widgets with nullable parameter'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  String thisStringIsNull;
  String thisStringIsNotNull = 'text';

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            // We often check if a parameter is not null and then pass the parameter to a widget to be built like this
            if (thisStringIsNull != null) Text(thisStringIsNull),
            if (thisStringIsNotNull != null) Text(thisStringIsNotNull),
            // if we had a way to return void instead of null the widget could just handle the null check internally.
            // simply returning null is not an option, but the null aware 
            // spread operator ...? allows for something like this:
            ...?nullableText(thisStringIsNotNull),
            ...?nullableText(thisStringIsNull),
            // I would prefer to have an operator which works at the parameter level 
            // like this: Text(?parameterCouldBeNull) - where the constructor is only called if 'parameterCouldBeNull != null'
          ],
        ),
      ),
    );
  }
}

List<Widget> nullableText(String text) {
  if (text == null) {
    return null;
  } else {
    return [Text(text)];
  }
}