NestedScrollView with issue

main.dart

import 'package:flutter/material.dart';

final Color darkBlue = Color.fromARGB(255, 18, 32, 47);

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        home:  NestedScrollView(
      headerSliverBuilder: (_, __) => <Widget>[
        SliverAppBar(
          expandedHeight: 220,
          pinned: true,
          flexibleSpace: Container(color: Colors.grey, height: 220,),
        ),
      ],
      body: ListView.builder(itemBuilder: (context, index) {
        return Padding(
            padding: const EdgeInsets.only(bottom: 24.0),
            child: _row());
      }, itemCount: 4,)
    ));
  }
  
  Widget _row() {
    return Container(color: Colors.green, height: 500);
  }
}