Почему во время выполнения этого кода отображается просто белый экран?

import 'package:dart_mssql/dart_mssql.dart';
import 'package:flutter/material.dart';

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

ListView treeView = ListView(
  children: [
    ExpansionTile(
      title: Text("Text"),
      children: <Widget>[
        ListTile(
          title: Text("Text"),
        )
      ],
      childrenPadding: EdgeInsets.fromLTRB(25, 0, 0, 0),
    ),
    ListTile(
      title: Text("Table"),
    )
  ],
  padding: EdgeInsets.zero,
);

class USU extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    ListTile tile = ListTile(
      title: Text(""),
    );
    treeView = new ListView(
      children: <Widget>[
        tile,
      ],
    );
    MaterialApp app = MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        appBar: AppBar(),
        drawer: Drawer(
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.stretch,
            children: <Widget>[
              DrawerHeader(
                child: Text("Drawer"),
                decoration: BoxDecoration(color: Colors.blue),
                margin: EdgeInsets.zero,
              ),
              Expanded(
                child: treeView,
              ),
            ],
          ),
        ),
      ),
    );
    return app;
  }
}

Добавив вот это код перестал работать

ListTile tile = ListTile(
      title: Text(""),
    );
    treeView = new ListView(
      children: <Widget>[
        tile,
      ],
    );

Вот ошибки

E/flutter (16146): [ERROR:flutter/shell/common/shell.cc(210)] Dart Error: Unknown library tag.error: library handler failed
E/flutter (16146): [ERROR:flutter/shell/common/engine.cc(220)] Could not prepare to run the isolate.
E/flutter (16146): [ERROR:flutter/shell/common/engine.cc(159)] Engine not prepare and launch isolate.
E/flutter (16146): [ERROR:flutter/shell/common/shell.cc(491)] Could not launch engine with configuration.