[ios][bug] BottomSheet with image

main.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey();

  void _showBottomSheet() {
    _scaffoldKey.currentState.showBottomSheet<Null>((BuildContext context) {
      return new Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          Image.asset(
            "assets/flutter.png",
          ),
        ],
      );
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: _scaffoldKey,
      appBar: AppBar(
        title: Text(widget.title),
      ),
      backgroundColor: Colors.red,
      body: RaisedButton(
        onPressed: _showBottomSheet,
        child: Text('Show BottomSheet'),
      )
    );
  }
}