`Scaffold.bottomSheet` issues

main.dart

import 'package:flutter/material.dart';

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

class BottomSheetApp extends StatefulWidget {
  @override
  _BottomSheetAppState createState() => _BottomSheetAppState();
}

class _BottomSheetAppState extends State<BottomSheetApp> {
  bool showsSheet = false;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: ElevatedButton(
            child: Text('Toggle sheet'),
            onPressed: () => setState(() => showsSheet = !showsSheet),
          ),
        ),
        bottomSheet: showsSheet ? Container(color: Colors.blue) : null,
      ),
    );
  }
}