anchor.diff:      packageConfigFile.readAsStringSync(),
       packageConfigFile.uri,
     );
  -  final Uri packageFileUri = packageConfig.resolve(packageUri);
  +  final Uri? packageFileUri = packageConfig.resolve(packageUri);
     final File packageFile = fs.file(packageFileUri);
     if (!packageFile.existsSync()) {
       print('File $packageFile does not exist - forbidden type has moved or been removed.');
  
positive.code: import 'package:args/args.dart';
  import 'package:file/file.dart';
  import 'package:file/local.dart';
  import 'package:meta/meta.dart';
  import 'package:package_config/package_config.dart';
  import 'package:path/path.dart' as path;
  import 'package:process/process.dart';
  
negative.code: // Copyright 2014 The Flutter Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  import 'dart:convert';
  import 'dart:io';
  