diff --git a/packages/flutter_tools/lib/src/asset.dart b/packages/flutter_tools/lib/src/asset.dart
index c5fa45ab289..ed42baea293 100644
--- a/packages/flutter_tools/lib/src/asset.dart
+++ b/packages/flutter_tools/lib/src/asset.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';
 
@@ -48,12 +46,12 @@ const List<Map<String, Object>> kMaterialFonts = <Map<String, Object>>[
 /// Injected factory class for spawning [AssetBundle] instances.
 abstract class AssetBundleFactory {
   /// The singleton instance, pulled from the [AppContext].
-  static AssetBundleFactory get instance => context.get<AssetBundleFactory>();
+  static AssetBundleFactory get instance => context.get<AssetBundleFactory>()!;
 
   static AssetBundleFactory defaultInstance({
-    @required Logger logger,
-    @required FileSystem fileSystem,
-    @required Platform platform,
+    required Logger logger,
+    required FileSystem fileSystem,
+    required Platform platform,
     bool splitDeferredAssets = false,
   }) => _ManifestAssetBundleFactory(logger: logger, fileSystem: fileSystem, platform: platform, splitDeferredAssets: splitDeferredAssets);
 
@@ -82,18 +80,18 @@ abstract class AssetBundle {
   /// Returns 0 for success; non-zero for failure.
   Future<int> build({
     String manifestPath = defaultManifestPath,
-    String assetDirPath,
-    @required String packagesPath,
+    String? assetDirPath,
+    required String packagesPath,
     bool deferredComponentsEnabled = false,
-    TargetPlatform targetPlatform,
+    TargetPlatform? targetPlatform,
   });
 }
 
 class _ManifestAssetBundleFactory implements AssetBundleFactory {
   _ManifestAssetBundleFactory({
-    @required Logger logger,
-    @required FileSystem fileSystem,
-    @required Platform platform,
+    required Logger logger,
+    required FileSystem fileSystem,
+    required Platform platform,
     bool splitDeferredAssets = false,
   }) : _logger = logger,
        _fileSystem = fileSystem,
@@ -114,9 +112,9 @@ class ManifestAssetBundle implements AssetBundle {
   /// Constructs an [ManifestAssetBundle] that gathers the set of assets from the
   /// pubspec.yaml manifest.
   ManifestAssetBundle({
-    @required Logger logger,
-    @required FileSystem fileSystem,
-    @required Platform platform,
+    required Logger logger,
+    required FileSystem fileSystem,
+    required Platform platform,
     bool splitDeferredAssets = false,
   }) : _logger = logger,
        _fileSystem = fileSystem,
@@ -144,7 +142,7 @@ class ManifestAssetBundle implements AssetBundle {
   // the current project.
   final Map<Uri, Directory> _wildcardDirectories = <Uri, Directory>{};
 
-  DateTime _lastBuildTimestamp;
+  DateTime? _lastBuildTimestamp;
 
   static const String _kAssetManifestJson = 'AssetManifest.json';
   static const String _kNoticeFile = 'NOTICES';
@@ -161,7 +159,7 @@ class ManifestAssetBundle implements AssetBundle {
 
   @override
   bool needsBuild({ String manifestPath = defaultManifestPath }) {
-    final DateTime lastBuildTimestamp = _lastBuildTimestamp;
+    final DateTime? lastBuildTimestamp = _lastBuildTimestamp;
     if (lastBuildTimestamp == null) {
       return true;
     }
@@ -192,10 +190,10 @@ class ManifestAssetBundle implements AssetBundle {
   @override
   Future<int> build({
     String manifestPath = defaultManifestPath,
-    String assetDirPath,
-    @required String packagesPath,
+    String? assetDirPath,
+    required String packagesPath,
     bool deferredComponentsEnabled = false,
-    TargetPlatform targetPlatform,
+    TargetPlatform? targetPlatform,
   }) async {
     assetDirPath ??= getAssetBuildDirectory();
     FlutterProject flutterProject;
@@ -244,7 +242,7 @@ class ManifestAssetBundle implements AssetBundle {
       if (flutterProject.linux.existsSync())
         flutterProject.linux.managedDirectory.path,
     ];
-    final Map<_Asset, List<_Asset>> assetVariants = _parseAssets(
+    final Map<_Asset, List<_Asset>>? assetVariants = _parseAssets(
       packageConfig,
       flutterManifest,
       wildcardDirectories,
@@ -274,7 +272,7 @@ class ManifestAssetBundle implements AssetBundle {
     }
 
     final bool includesMaterialFonts = flutterManifest.usesMaterialDesign;
-    final List<Map<String, dynamic>> fonts = _parseFonts(
+    final List<Map<String, Object?>> fonts = _parseFonts(
       flutterManifest,
       packageConfig,
       primary: true,
@@ -287,7 +285,7 @@ class ManifestAssetBundle implements AssetBundle {
       if (packageUri != null && packageUri.scheme == 'file') {
         final String packageManifestPath = _fileSystem.path.fromUri(packageUri.resolve('../pubspec.yaml'));
         inputFiles.add(_fileSystem.file(packageManifestPath));
-        final FlutterManifest packageFlutterManifest = FlutterManifest.createFromPath(
+        final FlutterManifest? packageFlutterManifest = FlutterManifest.createFromPath(
           packageManifestPath,
           logger: _logger,
           fileSystem: _fileSystem,
@@ -309,7 +307,7 @@ class ManifestAssetBundle implements AssetBundle {
         }
         final String packageBasePath = _fileSystem.path.dirname(packageManifestPath);
 
-        final Map<_Asset, List<_Asset>> packageAssets = _parseAssets(
+        final Map<_Asset, List<_Asset>>? packageAssets = _parseAssets(
           packageConfig,
           packageFlutterManifest,
           // Do not track wildcard directories for dependencies.
@@ -344,11 +342,12 @@ class ManifestAssetBundle implements AssetBundle {
     // asset in entries.
     for (final _Asset asset in assetVariants.keys) {
       final File assetFile = asset.lookupAssetFile(_fileSystem);
-      if (!assetFile.existsSync() && assetVariants[asset].isEmpty) {
+      final List<_Asset> variants = assetVariants[asset]!;
+      if (!assetFile.existsSync() && variants.isEmpty) {
         _logger.printStatus('Error detected in pubspec.yaml:', emphasis: true);
         _logger.printError('No file or variants found for $asset.\n');
         if (asset.package != null) {
-          _logger.printError('This asset was included from package ${asset.package.name}.');
+          _logger.printError('This asset was included from package ${asset.package?.name}.');
         }
         return 1;
       }
@@ -359,10 +358,10 @@ class ManifestAssetBundle implements AssetBundle {
       // "1x" resolution variant and if both exist then the explicit 1x
       // variant is preferred.
       if (assetFile.existsSync()) {
-        assert(!assetVariants[asset].contains(asset));
-        assetVariants[asset].insert(0, asset);
+        assert(!variants.contains(asset));
+        variants.insert(0, asset);
       }
-      for (final _Asset variant in assetVariants[asset]) {
+      for (final _Asset variant in variants) {
         final File variantFile = variant.lookupAssetFile(_fileSystem);
         inputFiles.add(variantFile);
         assert(variantFile.existsSync());
@@ -374,13 +373,14 @@ class ManifestAssetBundle implements AssetBundle {
     if (deferredComponentsAssetVariants != null) {
       for (final String componentName in deferredComponentsAssetVariants.keys) {
         deferredComponentsEntries[componentName] = <String, DevFSContent>{};
-        for (final _Asset asset in deferredComponentsAssetVariants[componentName].keys) {
+        final Map<_Asset, List<_Asset>> assetsMap = deferredComponentsAssetVariants[componentName]!;
+        for (final _Asset asset in assetsMap.keys) {
           final File assetFile = asset.lookupAssetFile(_fileSystem);
-          if (!assetFile.existsSync() && deferredComponentsAssetVariants[componentName][asset].isEmpty) {
+          if (!assetFile.existsSync() && assetsMap[asset]!.isEmpty) {
             _logger.printStatus('Error detected in pubspec.yaml:', emphasis: true);
             _logger.printError('No file or variants found for $asset.\n');
             if (asset.package != null) {
-              _logger.printError('This asset was included from package ${asset.package.name}.');
+              _logger.printError('This asset was included from package ${asset.package?.name}.');
             }
             return 1;
           }
@@ -391,13 +391,13 @@ class ManifestAssetBundle implements AssetBundle {
           // "1x" resolution variant and if both exist then the explicit 1x
           // variant is preferred.
           if (assetFile.existsSync()) {
-            assert(!deferredComponentsAssetVariants[componentName][asset].contains(asset));
-            deferredComponentsAssetVariants[componentName][asset].insert(0, asset);
+            assert(!assetsMap[asset]!.contains(asset));
+            assetsMap[asset]!.insert(0, asset);
           }
-          for (final _Asset variant in deferredComponentsAssetVariants[componentName][asset]) {
+          for (final _Asset variant in assetsMap[asset]!) {
             final File variantFile = variant.lookupAssetFile(_fileSystem);
             assert(variantFile.existsSync());
-            deferredComponentsEntries[componentName][variant.entryUri.path] ??= DevFSFileContent(variantFile);
+            deferredComponentsEntries[componentName]![variant.entryUri.path] ??= DevFSFileContent(variantFile);
           }
         }
       }
@@ -455,7 +455,7 @@ class ManifestAssetBundle implements AssetBundle {
       entries[key] = content;
       return;
     }
-    final DevFSStringContent oldContent = entries[key] as DevFSStringContent;
+    final DevFSStringContent? oldContent = entries[key] as DevFSStringContent?;
     if (oldContent?.string != content.string) {
       entries[key] = content;
     }
@@ -463,7 +463,7 @@ class ManifestAssetBundle implements AssetBundle {
 
   void _setLicenseIfChanged(
     String combinedLicenses,
-    TargetPlatform targetPlatform,
+    TargetPlatform? targetPlatform,
   ) {
     // On the web, don't compress the NOTICES file since the client doesn't have
     // dart:io to decompress it. So use the standard _setIfChanged to check if
@@ -478,7 +478,7 @@ class ManifestAssetBundle implements AssetBundle {
     // the uncompressed strings to not incur decompression/decoding while making
     // the comparison.
     if (!entries.containsKey(_kNoticeZippedFile) ||
-        (entries[_kNoticeZippedFile] as DevFSStringCompressingBytesContent)
+        (entries[_kNoticeZippedFile] as DevFSStringCompressingBytesContent?)
             ?.equals(combinedLicenses) != true) {
       entries[_kNoticeZippedFile] = DevFSStringCompressingBytesContent(
         combinedLicenses,
@@ -493,18 +493,18 @@ class ManifestAssetBundle implements AssetBundle {
   List<_Asset> _getMaterialAssets() {
     final List<_Asset> result = <_Asset>[];
     for (final Map<String, Object> family in kMaterialFonts) {
-      final Object fonts = family['fonts'];
+      final Object? fonts = family['fonts'];
       if (fonts == null) {
         continue;
       }
       for (final Map<String, Object> font in fonts as List<Map<String, String>>) {
-        final String asset = font['asset'] as String;
+        final String? asset = font['asset'] as String?;
         if (asset == null) {
           continue;
         }
         final Uri entryUri = _fileSystem.path.toUri(asset);
         result.add(_Asset(
-          baseDir: _fileSystem.path.join(Cache.flutterRoot, 'bin', 'cache', 'artifacts', 'material_fonts'),
+          baseDir: _fileSystem.path.join(Cache.flutterRoot!, 'bin', 'cache', 'artifacts', 'material_fonts'),
           relativeUri: Uri(path: entryUri.pathSegments.last),
           entryUri: entryUri,
           package: null,
@@ -515,13 +515,13 @@ class ManifestAssetBundle implements AssetBundle {
     return result;
   }
 
-  List<Map<String, dynamic>> _parseFonts(
+  List<Map<String, Object?>> _parseFonts(
     FlutterManifest manifest,
     PackageConfig packageConfig, {
-    String packageName,
-    @required bool primary,
+    String? packageName,
+    required bool primary,
   }) {
-    return <Map<String, dynamic>>[
+    return <Map<String, Object?>>[
       if (primary && manifest.usesMaterialDesign)
         ...kMaterialFonts,
       if (packageName == null)
@@ -543,7 +543,7 @@ class ManifestAssetBundle implements AssetBundle {
     Directory projectDirectory, {
     List<String> excludeDirs = const <String>[],
   }) {
-    final List<DeferredComponent> components = flutterManifest.deferredComponents;
+    final List<DeferredComponent>? components = flutterManifest.deferredComponents;
     final Map<String, Map<_Asset, List<_Asset>>> deferredComponentsAssetVariants = <String, Map<_Asset, List<_Asset>>>{};
     if (components == null) {
       return deferredComponentsAssetVariants;
@@ -559,7 +559,7 @@ class ManifestAssetBundle implements AssetBundle {
             flutterManifest,
             assetBasePath,
             cache,
-            deferredComponentsAssetVariants[component.name],
+            deferredComponentsAssetVariants[component.name]!,
             assetUri,
             excludeDirs: excludeDirs,
           );
@@ -569,7 +569,7 @@ class ManifestAssetBundle implements AssetBundle {
             flutterManifest,
             assetBasePath,
             cache,
-            deferredComponentsAssetVariants[component.name],
+            deferredComponentsAssetVariants[component.name]!,
             assetUri,
             excludeDirs: excludeDirs,
           );
@@ -604,7 +604,7 @@ class ManifestAssetBundle implements AssetBundle {
     final List<_Asset> sortedKeys = jsonEntries.keys.toList()
         ..sort((_Asset left, _Asset right) => left.entryUri.path.compareTo(right.entryUri.path));
     for (final _Asset main in sortedKeys) {
-      jsonObject[main.entryUri.path] = jsonEntries[main];
+      jsonObject[main.entryUri.path] = jsonEntries[main]!;
     }
     return DevFSStringContent(json.encode(jsonObject));
   }
@@ -623,7 +623,7 @@ class ManifestAssetBundle implements AssetBundle {
         final Uri assetUri = fontAsset.assetUri;
         if (assetUri.pathSegments.first == 'packages' &&
             !_fileSystem.isFileSync(_fileSystem.path.fromUri(
-              packageConfig[packageName]?.packageUriRoot?.resolve('../${assetUri.path}')))) {
+              packageConfig[packageName]?.packageUriRoot.resolve('../${assetUri.path}')))) {
           packageFontAssets.add(FontAsset(
             fontAsset.assetUri,
             weight: fontAsset.weight,
@@ -667,14 +667,14 @@ class ManifestAssetBundle implements AssetBundle {
   ///   ],
   /// }
   /// ```
-  Map<_Asset, List<_Asset>> _parseAssets(
+  Map<_Asset, List<_Asset>>? _parseAssets(
     PackageConfig packageConfig,
     FlutterManifest flutterManifest,
     List<Uri> wildcardDirectories,
     String assetBase, {
     List<String> excludeDirs = const <String>[],
-    String packageName,
-    Package attributedPackage,
+    String? packageName,
+    Package? attributedPackage,
   }) {
     final Map<_Asset, List<_Asset>> result = <_Asset, List<_Asset>>{};
 
@@ -737,8 +737,8 @@ class ManifestAssetBundle implements AssetBundle {
     Map<_Asset, List<_Asset>> result,
     Uri assetUri, {
     List<String> excludeDirs = const <String>[],
-    String packageName,
-    Package attributedPackage,
+    String? packageName,
+    Package? attributedPackage,
   }) {
     final String directoryPath = _fileSystem.path.join(
         assetBase, assetUri.toFilePath(windows: _platform.isWindows));
@@ -777,8 +777,8 @@ class ManifestAssetBundle implements AssetBundle {
     Map<_Asset, List<_Asset>> result,
     Uri assetUri, {
     List<String> excludeDirs = const <String>[],
-    String packageName,
-    Package attributedPackage,
+    String? packageName,
+    Package? attributedPackage,
   }) {
     final _Asset asset = _resolveAsset(
       packageConfig,
@@ -792,7 +792,7 @@ class ManifestAssetBundle implements AssetBundle {
     for (final String path in cache.variantsFor(assetFile.path)) {
       final String relativePath = _fileSystem.path.relative(path, from: asset.baseDir);
       final Uri relativeUri = _fileSystem.path.toUri(relativePath);
-      final Uri entryUri = asset.symbolicPrefixUri == null
+      final Uri? entryUri = asset.symbolicPrefixUri == null
           ? relativeUri
           : asset.symbolicPrefixUri?.resolveUri(relativeUri);
       if (entryUri != null) {
@@ -814,15 +814,15 @@ class ManifestAssetBundle implements AssetBundle {
     PackageConfig packageConfig,
     String assetsBaseDir,
     Uri assetUri,
-    String packageName,
-    Package attributedPackage,
+    String? packageName,
+    Package? attributedPackage,
   ) {
     final String assetPath = _fileSystem.path.fromUri(assetUri);
     if (assetUri.pathSegments.first == 'packages'
       && !_fileSystem.isFileSync(_fileSystem.path.join(assetsBaseDir, assetPath))) {
       // The asset is referenced in the pubspec.yaml as
       // 'packages/PACKAGE_NAME/PATH/TO/ASSET .
-      final _Asset packageAsset = _resolvePackageAsset(
+      final _Asset? packageAsset = _resolvePackageAsset(
         assetUri,
         packageConfig,
         attributedPackage,
@@ -842,12 +842,12 @@ class ManifestAssetBundle implements AssetBundle {
     );
   }
 
-  _Asset _resolvePackageAsset(Uri assetUri, PackageConfig packageConfig, Package attributedPackage) {
+  _Asset? _resolvePackageAsset(Uri assetUri, PackageConfig packageConfig, Package? attributedPackage) {
     assert(assetUri.pathSegments.first == 'packages');
     if (assetUri.pathSegments.length > 1) {
       final String packageName = assetUri.pathSegments[1];
-      final Package package = packageConfig[packageName];
-      final Uri packageUri = package?.packageUriRoot;
+      final Package? package = packageConfig[packageName];
+      final Uri? packageUri = package?.packageUriRoot;
       if (packageUri != null && packageUri.scheme == 'file') {
         return _Asset(
           baseDir: _fileSystem.path.fromUri(packageUri),
@@ -869,15 +869,15 @@ class ManifestAssetBundle implements AssetBundle {
 @immutable
 class _Asset {
   const _Asset({
-    @required this.baseDir,
-    @required this.relativeUri,
-    @required this.entryUri,
-    @required this.package,
+    required this.baseDir,
+    required this.relativeUri,
+    required this.entryUri,
+    required this.package,
   });
 
   final String baseDir;
 
-  final Package package;
+  final Package? package;
 
   /// A platform-independent URL where this asset can be found on disk on the
   /// host system relative to [baseDir].
@@ -892,7 +892,7 @@ class _Asset {
 
   /// The delta between what the entryUri is and the relativeUri (e.g.,
   /// packages/flutter_gallery).
-  Uri get symbolicPrefixUri {
+  Uri? get symbolicPrefixUri {
     if (entryUri == relativeUri) {
       return null;
     }
@@ -966,11 +966,11 @@ class _AssetDirectoryCache {
           continue;
         }
         variants[variantName] ??= <String>[];
-        variants[variantName].add(path);
+        variants[variantName]!.add(path);
       }
       _cache[directory] = variants;
     }
 
-    return _cache[directory][assetName] ?? const <String>[];
+    return _cache[directory]![assetName] ?? const <String>[];
   }
 }
diff --git a/packages/flutter_tools/lib/src/compile.dart b/packages/flutter_tools/lib/src/compile.dart
index 97176dfaa20..73da9c2d345 100644
--- a/packages/flutter_tools/lib/src/compile.dart
+++ b/packages/flutter_tools/lib/src/compile.dart
@@ -471,8 +471,8 @@ abstract class ResidentCompiler {
     List<Uri>? invalidatedFiles, {
     required String outputPath,
     required PackageConfig packageConfig,
-    required String projectRootPath,
     required FileSystem fs,
+    String? projectRootPath,
     bool suppressErrors = false,
     bool checkDartPluginRegistry = false,
   });
diff --git a/packages/flutter_tools/lib/src/devfs.dart b/packages/flutter_tools/lib/src/devfs.dart
index c254f5c3508..4aea017f700 100644
--- a/packages/flutter_tools/lib/src/devfs.dart
+++ b/packages/flutter_tools/lib/src/devfs.dart
@@ -2,11 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
-import 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';
 import 'package:vm_service/vm_service.dart' as vm_service;
 
@@ -29,7 +26,7 @@ class DevFSConfig {
   bool noDirectorySymlinks = false;
 }
 
-DevFSConfig get devFSConfig => context.get<DevFSConfig>();
+DevFSConfig? get devFSConfig => context.get<DevFSConfig>();
 
 /// Common superclass for content copied to the device.
 abstract class DevFSContent {
@@ -60,11 +57,11 @@ class DevFSFileContent extends DevFSContent {
   DevFSFileContent(this.file);
 
   final FileSystemEntity file;
-  File _linkTarget;
-  FileStat _fileStat;
+  File? _linkTarget;
+  FileStat? _fileStat;
 
   File _getFile() {
-    final File linkTarget = _linkTarget;
+    final File? linkTarget = _linkTarget;
     if (linkTarget != null) {
       return linkTarget;
     }
@@ -76,7 +73,7 @@ class DevFSFileContent extends DevFSContent {
   }
 
   void _stat() {
-    final File linkTarget = _linkTarget;
+    final File? linkTarget = _linkTarget;
     if (linkTarget != null) {
       // Stat the cached symlink target.
       final FileStat fileStat = linkTarget.statSync();
@@ -106,9 +103,9 @@ class DevFSFileContent extends DevFSContent {
 
   @override
   bool get isModified {
-    final FileStat oldFileStat = _fileStat;
+    final FileStat? oldFileStat = _fileStat;
     _stat();
-    final FileStat newFileStat = _fileStat;
+    final FileStat? newFileStat = _fileStat;
     if (oldFileStat == null && newFileStat == null) {
       return false;
     }
@@ -117,9 +114,9 @@ class DevFSFileContent extends DevFSContent {
 
   @override
   bool isModifiedAfter(DateTime time) {
-    final FileStat oldFileStat = _fileStat;
+    final FileStat? oldFileStat = _fileStat;
     _stat();
-    final FileStat newFileStat = _fileStat;
+    final FileStat? newFileStat = _fileStat;
     if (oldFileStat == null && newFileStat == null) {
       return false;
     }
@@ -218,7 +215,7 @@ class DevFSStringContent extends DevFSByteContent {
 /// The `hintString` parameter is a zlib dictionary hinting mechanism to suggest
 /// the most common string occurrences to potentially assist with compression.
 class DevFSStringCompressingBytesContent extends DevFSContent {
-  DevFSStringCompressingBytesContent(this._string, { String hintString })
+  DevFSStringCompressingBytesContent(this._string, { String? hintString })
     : _compressor = ZLibEncoder(
       dictionary: hintString == null
           ? null
@@ -231,10 +228,9 @@ class DevFSStringCompressingBytesContent extends DevFSContent {
   final ZLibEncoder _compressor;
   final DateTime _modificationTime = DateTime.now();
 
-  List<int> _bytes;
   bool _isModified = true;
 
-  List<int> get bytes => _bytes ??= _compressor.convert(utf8.encode(_string));
+  late final List<int> bytes = _compressor.convert(utf8.encode(_string));
 
   /// Return true only once so that the content is written to the device only once.
   @override
@@ -266,7 +262,7 @@ class DevFSException implements Exception {
   DevFSException(this.message, [this.error, this.stackTrace]);
   final String message;
   final dynamic error;
-  final StackTrace stackTrace;
+  final StackTrace? stackTrace;
 
   @override
   String toString() => 'DevFSException($message, $error, $stackTrace)';
@@ -286,10 +282,10 @@ class _DevFSHttpWriter implements DevFSWriter {
   _DevFSHttpWriter(
     this.fsName,
     FlutterVmService serviceProtocol, {
-    @required OperatingSystemUtils osUtils,
-    @required HttpClient httpClient,
-    @required Logger logger,
-    Duration uploadRetryThrottle,
+    required OperatingSystemUtils osUtils,
+    required HttpClient httpClient,
+    required Logger logger,
+    Duration? uploadRetryThrottle,
   })
     : httpAddress = serviceProtocol.httpAddress,
       _client = httpClient,
@@ -300,10 +296,10 @@ class _DevFSHttpWriter implements DevFSWriter {
   final HttpClient _client;
   final OperatingSystemUtils _osUtils;
   final Logger _logger;
-  final Duration _uploadRetryThrottle;
+  final Duration? _uploadRetryThrottle;
 
   final String fsName;
-  final Uri httpAddress;
+  final Uri? httpAddress;
 
   // 3 was chosen to try to limit the variance in the time it takes to execute
   // `await request.close()` since there is a known bug in Dart where it doesn't
@@ -312,11 +308,11 @@ class _DevFSHttpWriter implements DevFSWriter {
   static const int kMaxInFlight = 3;
 
   int _inFlight = 0;
-  Map<Uri, DevFSContent> _outstanding = <Uri, DevFSContent>{};
-  Completer<void> _completer = Completer<void>();
+  late Map<Uri, DevFSContent> _outstanding;
+  late Completer<void> _completer;
 
   @override
-  Future<void> write(Map<Uri, DevFSContent> entries, Uri devFSBase, [DevFSWriter parent]) async {
+  Future<void> write(Map<Uri, DevFSContent> entries, Uri devFSBase, [DevFSWriter? parent]) async {
     try {
       _client.maxConnectionsPerHost = kMaxInFlight;
       _completer = Completer<void>();
@@ -335,7 +331,7 @@ class _DevFSHttpWriter implements DevFSWriter {
   void _scheduleWrites() {
     while ((_inFlight < kMaxInFlight) && (!_completer.isCompleted) && _outstanding.isNotEmpty) {
       final Uri deviceUri = _outstanding.keys.first;
-      final DevFSContent content = _outstanding.remove(deviceUri);
+      final DevFSContent content = _outstanding.remove(deviceUri)!;
       _startWrite(deviceUri, content, retry: 10);
       _inFlight += 1;
     }
@@ -351,7 +347,7 @@ class _DevFSHttpWriter implements DevFSWriter {
   }) async {
     while(true) {
       try {
-        final HttpClientRequest request = await _client.putUrl(httpAddress);
+        final HttpClientRequest request = await _client.putUrl(httpAddress!);
         request.headers.removeAll(HttpHeaders.acceptEncodingHeader);
         request.headers.add('dev_fs_name', fsName);
         request.headers.add('dev_fs_uri_b64', base64.encode(utf8.encode('$deviceUri')));
@@ -424,7 +420,7 @@ class UpdateFSReport {
   Duration get findInvalidatedDuration => _findInvalidatedDuration;
 
   bool _success;
-  String fastReassembleClassName;
+  String? fastReassembleClassName;
   int _invalidatedSourcesCount;
   int _syncedBytes;
   int _scannedSourcesCount;
@@ -454,11 +450,11 @@ class DevFS {
     FlutterVmService serviceProtocol,
     this.fsName,
     this.rootDirectory, {
-    @required OperatingSystemUtils osUtils,
-    @required Logger logger,
-    @required FileSystem fileSystem,
-    HttpClient httpClient,
-    Duration uploadRetryThrottle,
+    required OperatingSystemUtils osUtils,
+    required Logger logger,
+    required FileSystem fileSystem,
+    HttpClient? httpClient,
+    Duration? uploadRetryThrottle,
     StopwatchFactory stopwatchFactory = const StopwatchFactory(),
   }) : _vmService = serviceProtocol,
        _logger = logger,
@@ -471,7 +467,7 @@ class DevFS {
         uploadRetryThrottle: uploadRetryThrottle,
         httpClient: httpClient ?? ((context.get<HttpClientFactory>() == null)
           ? HttpClient()
-          : context.get<HttpClientFactory>()())),
+          : context.get<HttpClientFactory>()!())),
        _stopwatchFactory = stopwatchFactory;
 
   final FlutterVmService _vmService;
@@ -488,13 +484,13 @@ class DevFS {
   bool hasSetAssetDirectory = false;
 
   List<Uri> sources = <Uri>[];
-  DateTime lastCompiled;
-  DateTime _previousCompiled;
-  PackageConfig lastPackageConfig;
-  File _widgetCacheOutputFile;
+  DateTime? lastCompiled;
+  DateTime? _previousCompiled;
+  PackageConfig? lastPackageConfig;
+  File? _widgetCacheOutputFile;
 
-  Uri _baseUri;
-  Uri get baseUri => _baseUri;
+  Uri? _baseUri;
+  Uri? get baseUri => _baseUri;
 
   Uri deviceUriToHostUri(Uri deviceUri) {
     final String deviceUriString = deviceUri.toString();
@@ -510,7 +506,7 @@ class DevFS {
     _logger.printTrace('DevFS: Creating new filesystem on the device ($_baseUri)');
     try {
       final vm_service.Response response = await _vmService.createDevFS(fsName);
-      _baseUri = Uri.parse(response.json['uri'] as String);
+      _baseUri = Uri.parse(response.json!['uri'] as String);
     } on vm_service.RPCError catch (rpcException) {
       if (rpcException.code == RPCErrorCodes.kServiceDisappeared) {
         // This can happen if the device has been disconnected, so translate to
@@ -526,10 +522,10 @@ class DevFS {
       _logger.printTrace('DevFS: Creating failed. Destroying and trying again');
       await destroy();
       final vm_service.Response response = await _vmService.createDevFS(fsName);
-      _baseUri = Uri.parse(response.json['uri'] as String);
+      _baseUri = Uri.parse(response.json!['uri'] as String);
     }
     _logger.printTrace('DevFS: Created new filesystem on the device ($_baseUri)');
-    return _baseUri;
+    return _baseUri!;
   }
 
   Future<void> destroy() async {
@@ -556,8 +552,8 @@ class DevFS {
   ///
   /// If any other changes were made, or there is an error scanning the file,
   /// return `null`.
-  String _checkIfSingleWidgetReloadApplied() {
-    final File widgetCacheOutputFile = _widgetCacheOutputFile;
+  String? _checkIfSingleWidgetReloadApplied() {
+    final File? widgetCacheOutputFile = _widgetCacheOutputFile;
     if (widgetCacheOutputFile != null && widgetCacheOutputFile.existsSync()) {
       final String widget = widgetCacheOutputFile.readAsStringSync().trim();
       if (widget.isNotEmpty) {
@@ -571,20 +567,20 @@ class DevFS {
   ///
   /// Returns the number of bytes synced.
   Future<UpdateFSReport> update({
-    @required Uri mainUri,
-    @required ResidentCompiler generator,
-    @required bool trackWidgetCreation,
-    @required String pathToReload,
-    @required List<Uri> invalidatedFiles,
-    @required PackageConfig packageConfig,
-    @required String dillOutputPath,
-    DevFSWriter devFSWriter,
-    String target,
-    AssetBundle bundle,
-    DateTime firstBuildTime,
+    required Uri mainUri,
+    required ResidentCompiler generator,
+    required bool trackWidgetCreation,
+    required String pathToReload,
+    required List<Uri> invalidatedFiles,
+    required PackageConfig packageConfig,
+    required String dillOutputPath,
+    DevFSWriter? devFSWriter,
+    String? target,
+    AssetBundle? bundle,
+    DateTime? firstBuildTime,
     bool bundleFirstUpload = false,
     bool fullRestart = false,
-    String projectRootPath,
+    String? projectRootPath,
   }) async {
     assert(trackWidgetCreation != null);
     assert(generator != null);
@@ -606,7 +602,7 @@ class DevFS {
     // Await the compiler response after checking if the bundle is updated. This allows the file
     // stating to be done while waiting for the frontend_server response.
     final Stopwatch compileTimer = _stopwatchFactory.createStopwatch('compile')..start();
-    final Future<CompilerOutput> pendingCompilerOutput = generator.recompile(
+    final Future<CompilerOutput?> pendingCompilerOutput = generator.recompile(
       mainUri,
       invalidatedFiles,
       outputPath: dillOutputPath,
@@ -614,7 +610,7 @@ class DevFS {
       projectRootPath: projectRootPath,
       packageConfig: packageConfig,
       checkDartPluginRegistry: true, // The entry point is assumed not to have changed.
-    ).then((CompilerOutput result) {
+    ).then((CompilerOutput? result) {
       compileTimer.stop();
       return result;
     });
@@ -641,7 +637,7 @@ class DevFS {
         }
       });
     }
-    final CompilerOutput compilerOutput = await pendingCompilerOutput;
+    final CompilerOutput? compilerOutput = await pendingCompilerOutput;
     if (compilerOutput == null || compilerOutput.errorCount > 0) {
       return UpdateFSReport(success: false);
     }
@@ -654,8 +650,8 @@ class DevFS {
     // Don't send full kernel file that would overwrite what VM already
     // started loading from.
     if (!bundleFirstUpload) {
-      final String compiledBinary = compilerOutput?.outputFilename;
-      if (compiledBinary != null && compiledBinary.isNotEmpty) {
+      final String compiledBinary = compilerOutput.outputFilename;
+      if (compiledBinary.isNotEmpty) {
         final Uri entryUri = _fileSystem.path.toUri(pathToReload);
         final DevFSFileContent content = DevFSFileContent(_fileSystem.file(compiledBinary));
         syncedBytes += content.size;
@@ -665,7 +661,7 @@ class DevFS {
     _logger.printTrace('Updating files.');
     final Stopwatch transferTimer = _stopwatchFactory.createStopwatch('transfer')..start();
     if (dirtyEntries.isNotEmpty) {
-      await (devFSWriter ?? _httpWriter).write(dirtyEntries, _baseUri, _httpWriter);
+      await (devFSWriter ?? _httpWriter).write(dirtyEntries, _baseUri!, _httpWriter);
     }
     transferTimer.stop();
     _logger.printTrace('DevFS: Sync finished');
@@ -693,16 +689,17 @@ class DevFS {
 /// Requires that the file system is the same for both the tool and application.
 class LocalDevFSWriter implements DevFSWriter {
   LocalDevFSWriter({
-    @required FileSystem fileSystem,
+    required FileSystem fileSystem,
   }) : _fileSystem = fileSystem;
 
   final FileSystem _fileSystem;
 
   @override
-  Future<void> write(Map<Uri, DevFSContent> entries, Uri baseUri, [DevFSWriter parent]) async {
+  Future<void> write(Map<Uri, DevFSContent> entries, Uri baseUri, [DevFSWriter? parent]) async {
     try {
-      for (final Uri uri in entries.keys) {
-        final DevFSContent devFSContent = entries[uri];
+      for (final MapEntry<Uri, DevFSContent> entry in entries.entries) {
+        final Uri uri = entry.key;
+        final DevFSContent devFSContent = entry.value;
         final File destination = _fileSystem.file(baseUri.resolveUri(uri));
         if (!destination.parent.existsSync()) {
           destination.parent.createSync(recursive: true);
diff --git a/packages/flutter_tools/lib/src/device.dart b/packages/flutter_tools/lib/src/device.dart
index 0e9d63e63a0..ad8eb6b9744 100644
--- a/packages/flutter_tools/lib/src/device.dart
+++ b/packages/flutter_tools/lib/src/device.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 import 'dart:math' as math;
 
@@ -25,7 +23,7 @@ import 'device_port_forwarder.dart';
 import 'project.dart';
 import 'vmservice.dart';
 
-DeviceManager get deviceManager => context.get<DeviceManager>();
+DeviceManager? get deviceManager => context.get<DeviceManager>();
 
 /// A description of the kind of workflow the device supports.
 class Category {
@@ -63,9 +61,9 @@ class PlatformType {
 /// A discovery mechanism for flutter-supported development devices.
 abstract class DeviceManager {
   DeviceManager({
-    @required Logger logger,
-    @required Terminal terminal,
-    @required UserMessages userMessages,
+    required Logger logger,
+    required Terminal terminal,
+    required UserMessages userMessages,
   }) : _logger = logger,
        _terminal = terminal,
        _userMessages = userMessages;
@@ -78,17 +76,17 @@ abstract class DeviceManager {
   /// of their methods are called.
   List<DeviceDiscovery> get deviceDiscoverers;
 
-  String _specifiedDeviceId;
+  String? _specifiedDeviceId;
 
   /// A user-specified device ID.
-  String get specifiedDeviceId {
+  String? get specifiedDeviceId {
     if (_specifiedDeviceId == null || _specifiedDeviceId == 'all') {
       return null;
     }
     return _specifiedDeviceId;
   }
 
-  set specifiedDeviceId(String id) {
+  set specifiedDeviceId(String? id) {
     _specifiedDeviceId = id;
   }
 
@@ -120,7 +118,7 @@ abstract class DeviceManager {
     // found quickly, we don't wait for all the discoverers to complete.
     final List<Device> prefixMatches = <Device>[];
     final Completer<Device> exactMatchCompleter = Completer<Device>();
-    final List<Future<List<Device>>> futureDevices = <Future<List<Device>>>[
+    final List<Future<List<Device>?>> futureDevices = <Future<List<Device>?>>[
       for (final DeviceDiscovery discoverer in _platformDiscoverers)
         if (!hasWellKnownId || discoverer.wellKnownIds.contains(specifiedDeviceId))
           discoverer
@@ -143,9 +141,9 @@ abstract class DeviceManager {
     ];
 
     // Wait for an exact match, or for all discoverers to return results.
-    await Future.any<dynamic>(<Future<dynamic>>[
+    await Future.any<Object>(<Future<Object>>[
       exactMatchCompleter.future,
-      Future.wait<List<Device>>(futureDevices),
+      Future.wait<List<Device>?>(futureDevices),
     ]);
 
     if (exactMatchCompleter.isCompleted) {
@@ -156,9 +154,11 @@ abstract class DeviceManager {
 
   /// Returns the list of connected devices, filtered by any user-specified device id.
   Future<List<Device>> getDevices() {
-    return hasSpecifiedDeviceId
-        ? getDevicesById(specifiedDeviceId)
-        : getAllConnectedDevices();
+    final String? id = specifiedDeviceId;
+    if (id == null) {
+      return getAllConnectedDevices();
+    }
+    return getDevicesById(id);
   }
 
   Iterable<DeviceDiscovery> get _platformDiscoverers {
@@ -176,7 +176,7 @@ abstract class DeviceManager {
   }
 
   /// Returns the list of all connected devices. Discards existing cache of devices.
-  Future<List<Device>> refreshAllConnectedDevices({ Duration timeout }) async {
+  Future<List<Device>> refreshAllConnectedDevices({ Duration? timeout }) async {
     final List<List<Device>> devices = await Future.wait<List<Device>>(<Future<List<Device>>>[
       for (final DeviceDiscovery discoverer in _platformDiscoverers)
         discoverer.discoverDevices(timeout: timeout),
@@ -214,7 +214,7 @@ abstract class DeviceManager {
   ///
   /// * If [flutterProject] is null, then assume the project supports all
   /// device types.
-  Future<List<Device>> findTargetDevices(FlutterProject flutterProject, { Duration timeout }) async {
+  Future<List<Device>> findTargetDevices(FlutterProject flutterProject, { Duration? timeout }) async {
     if (timeout != null) {
       // Reset the cache with the specified timeout.
       await refreshAllConnectedDevices(timeout: timeout);
@@ -338,7 +338,7 @@ abstract class DeviceDiscovery {
   Future<List<Device>> get devices;
 
   /// Return all connected devices. Discards existing cache of devices.
-  Future<List<Device>> discoverDevices({ Duration timeout });
+  Future<List<Device>> discoverDevices({ Duration? timeout });
 
   /// Gets a list of diagnostic messages pertaining to issues with any connected
   /// devices (will be an empty list if there are no issues).
@@ -366,11 +366,11 @@ abstract class PollingDeviceDiscovery extends DeviceDiscovery {
 
   @protected
   @visibleForTesting
-  ItemListNotifier<Device> deviceNotifier;
+  ItemListNotifier<Device>? deviceNotifier;
 
-  Timer _timer;
+  Timer? _timer;
 
-  Future<List<Device>> pollingGetDevices({ Duration timeout });
+  Future<List<Device>> pollingGetDevices({ Duration? timeout });
 
   void startPolling() {
     if (_timer == null) {
@@ -380,11 +380,11 @@ abstract class PollingDeviceDiscovery extends DeviceDiscovery {
     }
   }
 
-  Timer _initTimer(Duration pollingTimeout) {
+  Timer _initTimer(Duration? pollingTimeout) {
     return Timer(_pollingInterval, () async {
       try {
         final List<Device> devices = await pollingGetDevices(timeout: pollingTimeout);
-        deviceNotifier.updateWithNewList(devices);
+        deviceNotifier!.updateWithNewList(devices);
       } on TimeoutException {
         // Do nothing on a timeout.
       }
@@ -404,24 +404,24 @@ abstract class PollingDeviceDiscovery extends DeviceDiscovery {
   }
 
   @override
-  Future<List<Device>> discoverDevices({ Duration timeout }) {
+  Future<List<Device>> discoverDevices({ Duration? timeout }) {
     deviceNotifier = null;
     return _populateDevices(timeout: timeout);
   }
 
-  Future<List<Device>> _populateDevices({ Duration timeout }) async {
+  Future<List<Device>> _populateDevices({ Duration? timeout }) async {
     deviceNotifier ??= ItemListNotifier<Device>.from(await pollingGetDevices(timeout: timeout));
-    return deviceNotifier.items;
+    return deviceNotifier!.items;
   }
 
   Stream<Device> get onAdded {
     deviceNotifier ??= ItemListNotifier<Device>();
-    return deviceNotifier.onAdded;
+    return deviceNotifier!.onAdded;
   }
 
   Stream<Device> get onRemoved {
     deviceNotifier ??= ItemListNotifier<Device>();
-    return deviceNotifier.onRemoved;
+    return deviceNotifier!.onRemoved;
   }
 
   void dispose() => stopPolling();
@@ -436,9 +436,9 @@ abstract class PollingDeviceDiscovery extends DeviceDiscovery {
 /// the host operating system in the case of Flutter Desktop.
 abstract class Device {
   Device(this.id, {
-    @required this.category,
-    @required this.platformType,
-    @required this.ephemeral,
+    required this.category,
+    required this.platformType,
+    required this.ephemeral,
   });
 
   final String id;
@@ -534,7 +534,7 @@ abstract class Device {
   ///
   /// For example, the desktop device classes can use a writer which
   /// copies the files across the local file system.
-  DevFSWriter createDevFSWriter(
+  DevFSWriter? createDevFSWriter(
     covariant ApplicationPackage app,
     String userIdentifier,
   ) {
@@ -564,7 +564,7 @@ abstract class Device {
   void clearLogs();
 
   /// Optional device-specific artifact overrides.
-  OverrideArtifacts get artifactOverrides => null;
+  OverrideArtifacts? get artifactOverrides => null;
 
   /// Start an app package on the current device.
   ///
@@ -575,7 +575,7 @@ abstract class Device {
     String mainPath,
     String route,
     DebuggingOptions debuggingOptions,
-    Map<String, dynamic> platformArgs,
+    Map<String, Object?> platformArgs,
     bool prebuiltApplication = false,
     bool ipv6 = false,
     String userIdentifier,
@@ -817,8 +817,8 @@ class DebuggingOptions {
   final bool enableSoftwareRendering;
   final bool skiaDeterministicRendering;
   final bool traceSkia;
-  final String traceAllowlist;
-  final String traceSkiaAllowlist;
+  final String? traceAllowlist;
+  final String? traceSkiaAllowlist;
   final bool traceSystrace;
   final bool endlessTraceBuffer;
   final bool dumpSkpOnShaderCompilation;
@@ -826,14 +826,14 @@ class DebuggingOptions {
   final bool purgePersistentCache;
   final bool useTestFonts;
   final bool verboseSystemLogs;
-  final int hostVmServicePort;
-  final int deviceVmServicePort;
+  final int? hostVmServicePort;
+  final int? deviceVmServicePort;
   final bool disablePortPublication;
-  final int ddsPort;
-  final Uri devToolsServerAddress;
-  final String port;
-  final String hostname;
-  final bool webEnableExposeUrl;
+  final int? ddsPort;
+  final Uri? devToolsServerAddress;
+  final String? port;
+  final String? hostname;
+  final bool? webEnableExposeUrl;
   final bool webUseSseForDebugProxy;
   final bool webUseSseForDebugBackend;
   final bool webUseSseForInjectedClient;
@@ -846,13 +846,13 @@ class DebuggingOptions {
   final bool webRunHeadless;
 
   /// The port the browser should use for its debugging protocol.
-  final int webBrowserDebugPort;
+  final int? webBrowserDebugPort;
 
   /// Enable expression evaluation for web target.
   final bool webEnableExpressionEvaluation;
 
   /// A file where the VM Service URL should be written after the application is started.
-  final String vmserviceOutFile;
+  final String? vmserviceOutFile;
   final bool fastStart;
 
   final bool nullAssertions;
@@ -875,7 +875,7 @@ class LaunchResult {
   bool get hasObservatory => observatoryUri != null;
 
   final bool started;
-  final Uri observatoryUri;
+  final Uri? observatoryUri;
 
   @override
   String toString() {
@@ -896,13 +896,13 @@ abstract class DeviceLogReader {
 
   /// Some logs can be obtained from a VM service stream.
   /// Set this after the VM services are connected.
-  FlutterVmService connectedVMService;
+  FlutterVmService? connectedVMService;
 
   @override
   String toString() => name;
 
   /// Process ID of the app on the device.
-  int appPid;
+  int? appPid;
 
   // Clean up resources allocated by log reader e.g. subprocesses
   void dispose();
@@ -923,10 +923,10 @@ class NoOpDeviceLogReader implements DeviceLogReader {
   final String name;
 
   @override
-  int appPid;
+  int? appPid;
 
   @override
-  FlutterVmService connectedVMService;
+  FlutterVmService? connectedVMService;
 
   @override
   Stream<String> get logLines => const Stream<String>.empty();
@@ -939,7 +939,7 @@ class NoOpDeviceLogReader implements DeviceLogReader {
 /// [debuggingOptions.nullAssertions] is true.
 String computeDartVmFlags(DebuggingOptions debuggingOptions) {
   return <String>[
-    if (debuggingOptions.dartFlags?.isNotEmpty ?? false)
+    if (debuggingOptions.dartFlags.isNotEmpty)
       debuggingOptions.dartFlags,
     if (debuggingOptions.nullAssertions)
       '--null_assertions',
diff --git a/packages/flutter_tools/lib/src/vmservice.dart b/packages/flutter_tools/lib/src/vmservice.dart
index f626c704d48..89866f21469 100644
--- a/packages/flutter_tools/lib/src/vmservice.dart
+++ b/packages/flutter_tools/lib/src/vmservice.dart
@@ -2,11 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
-import 'package:meta/meta.dart' show required, visibleForTesting;
+import 'package:meta/meta.dart' show visibleForTesting;
 import 'package:vm_service/vm_service.dart' as vm_service;
 
 import 'base/common.dart';
@@ -31,7 +29,7 @@ const int kIsolateReloadBarred = 1005;
 
 /// Override `WebSocketConnector` in [context] to use a different constructor
 /// for [WebSocket]s (used by tests).
-typedef WebSocketConnector = Future<io.WebSocket> Function(String url, {io.CompressionOptions compression, @required Logger logger});
+typedef WebSocketConnector = Future<io.WebSocket> Function(String url, {io.CompressionOptions compression, required Logger logger});
 
 typedef PrintStructuredErrorLogMethod = void Function(vm_service.Event);
 
@@ -41,7 +39,7 @@ WebSocketConnector _openChannel = _defaultOpenChannel;
 ///
 /// Provide a `null` value to restore the original connector.
 @visibleForTesting
-set openChannelForTesting(WebSocketConnector connector) {
+set openChannelForTesting(WebSocketConnector? connector) {
   _openChannel = connector ?? _defaultOpenChannel;
 }
 
@@ -93,7 +91,7 @@ typedef CompileExpression = Future<String> Function(
   List<String> definitions,
   List<String> typeDefinitions,
   String libraryUri,
-  String klass,
+  String? klass,
   bool isStatic,
 );
 
@@ -104,13 +102,13 @@ typedef GetSkSLMethod = Future<String> Function();
 
 Future<io.WebSocket> _defaultOpenChannel(String url, {
   io.CompressionOptions compression = io.CompressionOptions.compressionDefault,
-  @required Logger logger,
+  required Logger logger,
 }) async {
   Duration delay = const Duration(milliseconds: 100);
   int attempts = 0;
-  io.WebSocket socket;
+  io.WebSocket? socket;
 
-  Future<void> handleError(dynamic e) async {
+  Future<void> handleError(Object? e) async {
     void Function(String) printVisibleTrace = logger.printTrace;
     if (attempts == 10) {
       logger.printStatus('Connecting to the VM Service is taking longer than expected...');
@@ -142,7 +140,7 @@ Future<io.WebSocket> _defaultOpenChannel(String url, {
 
   final WebSocketConnector constructor = context.get<WebSocketConnector>() ?? (String url, {
     io.CompressionOptions compression = io.CompressionOptions.compressionDefault,
-    @required Logger logger,
+    Logger? logger,
   }) => io.WebSocket.connect(url, compression: compression);
 
   while (socket == null) {
@@ -161,14 +159,14 @@ Future<io.WebSocket> _defaultOpenChannel(String url, {
 /// Override `VMServiceConnector` in [context] to return a different VMService
 /// from [VMService.connect] (used by tests).
 typedef VMServiceConnector = Future<FlutterVmService> Function(Uri httpUri, {
-  ReloadSources reloadSources,
-  Restart restart,
-  CompileExpression compileExpression,
-  GetSkSLMethod getSkSLMethod,
-  PrintStructuredErrorLogMethod printStructuredErrorLogMethod,
+  ReloadSources? reloadSources,
+  Restart? restart,
+  CompileExpression? compileExpression,
+  GetSkSLMethod? getSkSLMethod,
+  PrintStructuredErrorLogMethod? printStructuredErrorLogMethod,
   io.CompressionOptions compression,
-  Device device,
-  @required Logger logger,
+  Device? device,
+  required Logger logger,
 });
 
 /// Set up the VM Service client by attaching services for each of the provided
@@ -176,12 +174,12 @@ typedef VMServiceConnector = Future<FlutterVmService> Function(Uri httpUri, {
 ///
 /// All parameters besides [vmService] may be null.
 Future<vm_service.VmService> setUpVmService(
-  ReloadSources reloadSources,
-  Restart restart,
-  CompileExpression compileExpression,
-  Device device,
-  GetSkSLMethod skSLMethod,
-  PrintStructuredErrorLogMethod printStructuredErrorLogMethod,
+  ReloadSources? reloadSources,
+  Restart? restart,
+  CompileExpression? compileExpression,
+  Device? device,
+  GetSkSLMethod? skSLMethod,
+  PrintStructuredErrorLogMethod? printStructuredErrorLogMethod,
   vm_service.VmService vmService
 ) async {
   // Each service registration requires a request to the attached VM service. Since the
@@ -189,14 +187,14 @@ Future<vm_service.VmService> setUpVmService(
   // all at the end of this method.
   final List<Future<vm_service.Success>> registrationRequests = <Future<vm_service.Success>>[];
   if (reloadSources != null) {
-    vmService.registerServiceCallback('reloadSources', (Map<String, dynamic> params) async {
+    vmService.registerServiceCallback('reloadSources', (Map<String, Object?> params) async {
       final String isolateId = _validateRpcStringParam('reloadSources', params, 'isolateId');
       final bool force = _validateRpcBoolParam('reloadSources', params, 'force');
       final bool pause = _validateRpcBoolParam('reloadSources', params, 'pause');
 
       await reloadSources(isolateId, force: force, pause: pause);
 
-      return <String, dynamic>{
+      return <String, Object>{
         'result': <String, Object>{
           'type': 'Success',
         }
@@ -206,10 +204,10 @@ Future<vm_service.VmService> setUpVmService(
   }
 
   if (restart != null) {
-    vmService.registerServiceCallback('hotRestart', (Map<String, dynamic> params) async {
+    vmService.registerServiceCallback('hotRestart', (Map<String, Object?> params) async {
       final bool pause = _validateRpcBoolParam('compileExpression', params, 'pause');
       await restart(pause: pause);
-      return <String, dynamic>{
+      return <String, Object>{
         'result': <String, Object>{
           'type': 'Success',
         }
@@ -218,12 +216,12 @@ Future<vm_service.VmService> setUpVmService(
     registrationRequests.add(vmService.registerService('hotRestart', 'Flutter Tools'));
   }
 
-  vmService.registerServiceCallback('flutterVersion', (Map<String, dynamic> params) async {
+  vmService.registerServiceCallback('flutterVersion', (Map<String, Object?> params) async {
     final FlutterVersion version = context.get<FlutterVersion>() ?? FlutterVersion();
     final Map<String, Object> versionJson = version.toJson();
     versionJson['frameworkRevisionShort'] = version.frameworkRevisionShort;
     versionJson['engineRevisionShort'] = version.engineRevisionShort;
-    return <String, dynamic>{
+    return <String, Object>{
       'result': <String, Object>{
         'type': 'Success',
         ...versionJson,
@@ -233,29 +231,29 @@ Future<vm_service.VmService> setUpVmService(
   registrationRequests.add(vmService.registerService('flutterVersion', 'Flutter Tools'));
 
   if (compileExpression != null) {
-    vmService.registerServiceCallback('compileExpression', (Map<String, dynamic> params) async {
+    vmService.registerServiceCallback('compileExpression', (Map<String, Object?> params) async {
       final String isolateId = _validateRpcStringParam('compileExpression', params, 'isolateId');
       final String expression = _validateRpcStringParam('compileExpression', params, 'expression');
-      final List<String> definitions = List<String>.from(params['definitions'] as List<dynamic>);
-      final List<String> typeDefinitions = List<String>.from(params['typeDefinitions'] as List<dynamic>);
-      final String libraryUri = params['libraryUri'] as String;
-      final String klass = params['klass'] as String;
+      final List<String> definitions = List<String>.from(params['definitions']! as List<Object?>);
+      final List<String> typeDefinitions = List<String>.from(params['typeDefinitions']! as List<Object?>);
+      final String libraryUri = params['libraryUri']! as String;
+      final String? klass = params['klass'] as String?;
       final bool isStatic = _validateRpcBoolParam('compileExpression', params, 'isStatic');
 
       final String kernelBytesBase64 = await compileExpression(isolateId,
           expression, definitions, typeDefinitions, libraryUri, klass,
           isStatic);
-      return <String, dynamic>{
+      return <String, Object>{
         'type': 'Success',
-        'result': <String, dynamic>{'kernelBytes': kernelBytesBase64},
+        'result': <String, String>{'kernelBytes': kernelBytesBase64},
       };
     });
     registrationRequests.add(vmService.registerService('compileExpression', 'Flutter Tools'));
   }
   if (device != null) {
-    vmService.registerServiceCallback('flutterMemoryInfo', (Map<String, dynamic> params) async {
+    vmService.registerServiceCallback('flutterMemoryInfo', (Map<String, Object?> params) async {
       final MemoryInfo result = await device.queryMemoryInfo();
-      return <String, dynamic>{
+      return <String, Object>{
         'result': <String, Object>{
           'type': 'Success',
           ...result.toJson(),
@@ -265,9 +263,9 @@ Future<vm_service.VmService> setUpVmService(
     registrationRequests.add(vmService.registerService('flutterMemoryInfo', 'Flutter Tools'));
   }
   if (skSLMethod != null) {
-    vmService.registerServiceCallback('flutterGetSkSL', (Map<String, dynamic> params) async {
+    vmService.registerServiceCallback('flutterGetSkSL', (Map<String, Object?> params) async {
       final String filename = await skSLMethod();
-      return <String, dynamic>{
+      return <String, Object>{
         'result': <String, Object>{
           'type': 'Success',
           'filename': filename,
@@ -282,7 +280,7 @@ Future<vm_service.VmService> setUpVmService(
     // thrown if we're already subscribed.
     registrationRequests.add(vmService
       .streamListen(vm_service.EventStreams.kExtension)
-      .catchError((dynamic error) {}, test: (dynamic error) => error is vm_service.RPCError)
+      .catchError((Object? error) {}, test: (Object? error) => error is vm_service.RPCError)
     );
   }
 
@@ -304,14 +302,14 @@ Future<vm_service.VmService> setUpVmService(
 /// See: https://github.com/dart-lang/sdk/commit/df8bf384eb815cf38450cb50a0f4b62230fba217
 Future<FlutterVmService> connectToVmService(
   Uri httpUri, {
-    ReloadSources reloadSources,
-    Restart restart,
-    CompileExpression compileExpression,
-    GetSkSLMethod getSkSLMethod,
-    PrintStructuredErrorLogMethod printStructuredErrorLogMethod,
+    ReloadSources? reloadSources,
+    Restart? restart,
+    CompileExpression? compileExpression,
+    GetSkSLMethod? getSkSLMethod,
+    PrintStructuredErrorLogMethod? printStructuredErrorLogMethod,
     io.CompressionOptions compression = io.CompressionOptions.compressionDefault,
-    Device device,
-    @required Logger logger,
+    Device? device,
+    required Logger logger,
   }) async {
   final VMServiceConnector connector = context.get<VMServiceConnector>() ?? _connect;
   return connector(httpUri,
@@ -329,7 +327,7 @@ Future<FlutterVmService> connectToVmService(
 Future<vm_service.VmService> createVmServiceDelegate(
   Uri wsUri, {
   io.CompressionOptions compression = io.CompressionOptions.compressionDefault,
-  @required Logger logger,
+  required Logger logger,
 }) async {
   final io.WebSocket channel = await _openChannel(wsUri.toString(), compression: compression, logger: logger);
   return vm_service.VmService(
@@ -344,14 +342,14 @@ Future<vm_service.VmService> createVmServiceDelegate(
 
 Future<FlutterVmService> _connect(
   Uri httpUri, {
-  ReloadSources reloadSources,
-  Restart restart,
-  CompileExpression compileExpression,
-  GetSkSLMethod getSkSLMethod,
-  PrintStructuredErrorLogMethod printStructuredErrorLogMethod,
+  ReloadSources? reloadSources,
+  Restart? restart,
+  CompileExpression? compileExpression,
+  GetSkSLMethod? getSkSLMethod,
+  PrintStructuredErrorLogMethod? printStructuredErrorLogMethod,
   io.CompressionOptions compression = io.CompressionOptions.compressionDefault,
-  Device device,
-  @required Logger logger,
+  Device? device,
+  required Logger logger,
 }) async {
   final Uri wsUri = httpUri.replace(scheme: 'ws', path: urlContext.join(httpUri.path, 'ws'));
   final vm_service.VmService delegateService = await createVmServiceDelegate(
@@ -374,20 +372,20 @@ Future<FlutterVmService> _connect(
   return FlutterVmService(service, httpAddress: httpUri, wsAddress: wsUri);
 }
 
-String _validateRpcStringParam(String methodName, Map<String, dynamic> params, String paramName) {
-  final dynamic value = params[paramName];
-  if (value is! String || (value as String).isEmpty) {
+String _validateRpcStringParam(String methodName, Map<String, Object?> params, String paramName) {
+  final Object? value = params[paramName];
+  if (value is! String || value.isEmpty) {
     throw vm_service.RPCError(
       methodName,
       RPCErrorCodes.kInvalidParams,
       "Invalid '$paramName': $value",
     );
   }
-  return value as String;
+  return value;
 }
 
-bool _validateRpcBoolParam(String methodName, Map<String, dynamic> params, String paramName) {
-  final dynamic value = params[paramName];
+bool _validateRpcBoolParam(String methodName, Map<String, Object?> params, String paramName) {
+  final Object? value = params[paramName];
   if (value != null && value is! bool) {
     throw vm_service.RPCError(
       methodName,
@@ -395,30 +393,30 @@ bool _validateRpcBoolParam(String methodName, Map<String, dynamic> params, Strin
       "Invalid '$paramName': $value",
     );
   }
-  return (value as bool) ?? false;
+  return (value as bool?) ?? false;
 }
 
 /// Peered to an Android/iOS FlutterView widget on a device.
 class FlutterView {
   FlutterView({
-    @required this.id,
-    @required this.uiIsolate,
+    required this.id,
+    required this.uiIsolate,
   });
 
   factory FlutterView.parse(Map<String, Object> json) {
-    final Map<String, Object> rawIsolate = json['isolate'] as Map<String, Object>;
-    vm_service.IsolateRef isolate;
+    final Map<String, Object?>? rawIsolate = json['isolate'] as Map<String, Object?>?;
+    vm_service.IsolateRef? isolate;
     if (rawIsolate != null) {
       rawIsolate['number'] = rawIsolate['number']?.toString();
       isolate = vm_service.IsolateRef.parse(rawIsolate);
     }
     return FlutterView(
-      id: json['id'] as String,
+      id: json['id']! as String,
       uiIsolate: isolate,
     );
   }
 
-  final vm_service.IsolateRef uiIsolate;
+  final vm_service.IsolateRef? uiIsolate;
   final String id;
 
   bool get hasIsolate => uiIsolate != null;
@@ -426,8 +424,8 @@ class FlutterView {
   @override
   String toString() => id;
 
-  Map<String, Object> toJson() {
-    return <String, Object>{
+  Map<String, Object?> toJson() {
+    return <String, Object?>{
       'id': id,
       'isolate': uiIsolate?.toJson(),
     };
@@ -436,16 +434,20 @@ class FlutterView {
 
 /// Flutter specific VM Service functionality.
 class FlutterVmService {
-  FlutterVmService(this.service, {this.wsAddress, this.httpAddress});
+  FlutterVmService(
+    this.service, {
+    this.wsAddress,
+    this.httpAddress,
+  });
 
   final vm_service.VmService service;
-  final Uri wsAddress;
-  final Uri httpAddress;
+  final Uri? wsAddress;
+  final Uri? httpAddress;
 
-  Future<vm_service.Response> callMethodWrapper(
+  Future<vm_service.Response?> callMethodWrapper(
     String method, {
-    String isolateId,
-    Map<String, dynamic> args
+    String? isolateId,
+    Map<String, Object?>? args
   }) async {
     try {
       return await service.callMethod(method, isolateId: isolateId, args: args);
@@ -463,14 +465,13 @@ class FlutterVmService {
 
   /// Set the asset directory for the an attached Flutter view.
   Future<void> setAssetDirectory({
-    @required Uri assetsDirectory,
-    @required String viewId,
-    @required String uiIsolateId,
+    required Uri assetsDirectory,
+    required String? viewId,
+    required String? uiIsolateId,
   }) async {
-    assert(assetsDirectory != null);
     await callMethodWrapper(kSetAssetBundlePathMethod,
       isolateId: uiIsolateId,
-      args: <String, dynamic>{
+      args: <String, Object?>{
         'viewId': viewId,
         'assetDirectory': assetsDirectory.toFilePath(windows: false),
       });
@@ -480,10 +481,10 @@ class FlutterVmService {
   ///
   /// This method will only return data if `--cache-sksl` was provided as a
   /// flutter run argument, and only then on physical devices.
-  Future<Map<String, Object>> getSkSLs({
-    @required String viewId,
+  Future<Map<String, Object>?> getSkSLs({
+    required String viewId,
   }) async {
-    final vm_service.Response response = await callMethodWrapper(
+    final vm_service.Response? response = await callMethodWrapper(
       kGetSkSLsMethod,
       args: <String, String>{
         'viewId': viewId,
@@ -492,14 +493,14 @@ class FlutterVmService {
     if (response == null) {
       return null;
     }
-    return response.json['SkSLs'] as Map<String, Object>;
+    return response.json?['SkSLs'] as Map<String, Object>?;
   }
 
   /// Flush all tasks on the UI thread for an attached Flutter view.
   ///
   /// This method is currently used only for benchmarking.
   Future<void> flushUIThreadTasks({
-    @required String uiIsolateId,
+    required String uiIsolateId,
   }) async {
     await callMethodWrapper(
       kFlushUIThreadTasksMethod,
@@ -515,9 +516,9 @@ class FlutterVmService {
   /// This method is used by the tool to hot restart an already running Flutter
   /// engine.
   Future<void> runInView({
-    @required String viewId,
-    @required Uri main,
-    @required Uri assetsDirectory,
+    required String viewId,
+    required Uri main,
+    required Uri assetsDirectory,
   }) async {
     try {
       await service.streamListen(vm_service.EventStreams.kIsolate);
@@ -539,60 +540,63 @@ class FlutterVmService {
   }
 
   Future<String> flutterDebugDumpApp({
-    @required String isolateId,
+    required String isolateId,
   }) async {
-    final Map<String, Object> response = await invokeFlutterExtensionRpcRaw(
+    final Map<String, Object?>? response = await invokeFlutterExtensionRpcRaw(
       'ext.flutter.debugDumpApp',
       isolateId: isolateId,
     );
-    return response != null ? response['data']?.toString() : '';
+    return response?['data']?.toString() ?? '';
   }
 
   Future<String> flutterDebugDumpRenderTree({
-    @required String isolateId,
+    required String isolateId,
   }) async {
-    final Map<String, Object> response = await invokeFlutterExtensionRpcRaw(
+    final Map<String, Object?>? response = await invokeFlutterExtensionRpcRaw(
       'ext.flutter.debugDumpRenderTree',
       isolateId: isolateId,
       args: <String, Object>{}
     );
-    return response != null ? response['data']?.toString() : '';
+    return response?['data']?.toString() ?? '';
   }
 
   Future<String> flutterDebugDumpLayerTree({
-    @required String isolateId,
+    required String isolateId,
   }) async {
-    final Map<String, Object> response = await invokeFlutterExtensionRpcRaw(
+    final Map<String, Object?>? response = await invokeFlutterExtensionRpcRaw(
       'ext.flutter.debugDumpLayerTree',
       isolateId: isolateId,
     );
-    return response != null ? response['data']?.toString() : '';
+    return response?['data']?.toString() ?? '';
   }
 
   Future<String> flutterDebugDumpSemanticsTreeInTraversalOrder({
-    @required String isolateId,
+    required String isolateId,
   }) async {
-    final Map<String, Object> response = await invokeFlutterExtensionRpcRaw(
+    final Map<String, Object?>? response = await invokeFlutterExtensionRpcRaw(
       'ext.flutter.debugDumpSemanticsTreeInTraversalOrder',
       isolateId: isolateId,
     );
-    return response != null ? response['data']?.toString() : '';
+    return response?['data']?.toString() ?? '';
   }
 
   Future<String> flutterDebugDumpSemanticsTreeInInverseHitTestOrder({
-    @required String isolateId,
+    required String isolateId,
   }) async {
-    final Map<String, Object> response = await invokeFlutterExtensionRpcRaw(
+    final Map<String, Object?>? response = await invokeFlutterExtensionRpcRaw(
       'ext.flutter.debugDumpSemanticsTreeInInverseHitTestOrder',
       isolateId: isolateId,
     );
-    return response != null ? response['data']?.toString() : '';
+    if (response != null) {
+      return response['data']?.toString() ?? '';
+    }
+    return '';
   }
 
-  Future<Map<String, dynamic>> _flutterToggle(String name, {
-    @required String isolateId,
+  Future<Map<String, Object?>?> _flutterToggle(String name, {
+    required String isolateId,
   }) async {
-    Map<String, dynamic> state = await invokeFlutterExtensionRpcRaw(
+    Map<String, Object?>? state = await invokeFlutterExtensionRpcRaw(
       'ext.flutter.$name',
       isolateId: isolateId,
     );
@@ -600,7 +604,7 @@ class FlutterVmService {
       state = await invokeFlutterExtensionRpcRaw(
         'ext.flutter.$name',
         isolateId: isolateId,
-        args: <String, dynamic>{
+        args: <String, Object>{
           'enabled': state['enabled'] == 'true' ? 'false' : 'true',
         },
       );
@@ -609,38 +613,38 @@ class FlutterVmService {
     return state;
   }
 
-  Future<Map<String, dynamic>> flutterToggleDebugPaintSizeEnabled({
-    @required String isolateId,
+  Future<Map<String, Object?>?> flutterToggleDebugPaintSizeEnabled({
+    required String isolateId,
   }) => _flutterToggle('debugPaint', isolateId: isolateId);
 
-  Future<Map<String, dynamic>> flutterTogglePerformanceOverlayOverride({
-    @required String isolateId,
+  Future<Map<String, Object?>?> flutterTogglePerformanceOverlayOverride({
+    required String isolateId,
   }) => _flutterToggle('showPerformanceOverlay', isolateId: isolateId);
 
-  Future<Map<String, dynamic>> flutterToggleWidgetInspector({
-    @required String isolateId,
+  Future<Map<String, Object?>?> flutterToggleWidgetInspector({
+    required String isolateId,
   }) => _flutterToggle('inspector.show', isolateId: isolateId);
 
-  Future<Map<String,dynamic>> flutterToggleInvertOversizedImages({
-    @required String isolateId,
+  Future<Map<String, Object?>?> flutterToggleInvertOversizedImages({
+    required String isolateId,
   }) => _flutterToggle('invertOversizedImages', isolateId: isolateId);
 
-  Future<Map<String, dynamic>> flutterToggleProfileWidgetBuilds({
-    @required String isolateId,
+  Future<Map<String, Object?>?> flutterToggleProfileWidgetBuilds({
+    required String isolateId,
   }) => _flutterToggle('profileWidgetBuilds', isolateId: isolateId);
 
-  Future<Map<String, dynamic>> flutterDebugAllowBanner(bool show, {
-    @required String isolateId,
+  Future<Map<String, Object?>?> flutterDebugAllowBanner(bool show, {
+    required String isolateId,
   }) {
     return invokeFlutterExtensionRpcRaw(
       'ext.flutter.debugAllowBanner',
       isolateId: isolateId,
-      args: <String, dynamic>{'enabled': show ? 'true' : 'false'},
+      args: <String, Object>{'enabled': show ? 'true' : 'false'},
     );
   }
 
-  Future<Map<String, dynamic>> flutterReassemble({
-    @required String isolateId,
+  Future<Map<String, Object?>?> flutterReassemble({
+    required String isolateId,
   }) {
     return invokeFlutterExtensionRpcRaw(
       'ext.flutter.reassemble',
@@ -648,9 +652,9 @@ class FlutterVmService {
     );
   }
 
-  Future<Map<String, dynamic>> flutterFastReassemble({
-   @required String isolateId,
-   @required String className,
+  Future<Map<String, Object?>?> flutterFastReassemble({
+   required String isolateId,
+   required String className,
   }) {
     return invokeFlutterExtensionRpcRaw(
       'ext.flutter.fastReassemble',
@@ -662,18 +666,18 @@ class FlutterVmService {
   }
 
   Future<bool> flutterAlreadyPaintedFirstUsefulFrame({
-    @required String isolateId,
+    required String isolateId,
   }) async {
-    final Map<String, dynamic> result = await invokeFlutterExtensionRpcRaw(
+    final Map<String, Object?>? result = await invokeFlutterExtensionRpcRaw(
       'ext.flutter.didSendFirstFrameRasterizedEvent',
       isolateId: isolateId,
     );
     // result might be null when the service extension is not initialized
-    return result != null && result['enabled'] == 'true';
+    return result?['enabled'] == 'true';
   }
 
-  Future<Map<String, dynamic>> uiWindowScheduleFrame({
-    @required String isolateId,
+  Future<Map<String, Object?>?> uiWindowScheduleFrame({
+    required String isolateId,
   }) {
     return invokeFlutterExtensionRpcRaw(
       'ext.ui.window.scheduleFrame',
@@ -681,13 +685,13 @@ class FlutterVmService {
     );
   }
 
-  Future<Map<String, dynamic>> flutterEvictAsset(String assetPath, {
-   @required String isolateId,
+  Future<Map<String, Object?>?> flutterEvictAsset(String assetPath, {
+   required String isolateId,
   }) {
     return invokeFlutterExtensionRpcRaw(
       'ext.flutter.evict',
       isolateId: isolateId,
-      args: <String, dynamic>{
+      args: <String, Object?>{
         'value': assetPath,
       },
     );
@@ -698,10 +702,10 @@ class FlutterVmService {
   /// This method is only supported by certain embedders. This is
   /// described by [Device.supportsFlutterExit].
   Future<bool> flutterExit({
-    @required String isolateId,
+    required String isolateId,
   }) async {
     try {
-      final Map<String, Object> result = await invokeFlutterExtensionRpcRaw(
+      final Map<String, Object?>? result = await invokeFlutterExtensionRpcRaw(
         'ext.flutter.exit',
         isolateId: isolateId,
       );
@@ -725,18 +729,18 @@ class FlutterVmService {
   /// If a non-null value is provided for [platform], the platform override
   /// is updated with this value.
   Future<String> flutterPlatformOverride({
-    String platform,
-    @required String isolateId,
+    String? platform,
+    required String isolateId,
   }) async {
-    final Map<String, dynamic> result = await invokeFlutterExtensionRpcRaw(
+    final Map<String, Object?>? result = await invokeFlutterExtensionRpcRaw(
       'ext.flutter.platformOverride',
       isolateId: isolateId,
       args: platform != null
-        ? <String, dynamic>{'value': platform}
+        ? <String, Object>{'value': platform}
         : <String, String>{},
     );
     if (result != null && result['value'] is String) {
-      return result['value'] as String;
+      return result['value']! as String;
     }
     return 'unknown';
   }
@@ -746,15 +750,15 @@ class FlutterVmService {
   ///
   /// If a non-null value is provided for [brightness], the brightness override
   /// is updated with this value.
-  Future<Brightness> flutterBrightnessOverride({
-    Brightness brightness,
-    @required String isolateId,
+  Future<Brightness?> flutterBrightnessOverride({
+    Brightness? brightness,
+    required String isolateId,
   }) async {
-    final Map<String, dynamic> result = await invokeFlutterExtensionRpcRaw(
+    final Map<String, Object?>? result = await invokeFlutterExtensionRpcRaw(
       'ext.flutter.brightnessOverride',
       isolateId: isolateId,
       args: brightness != null
-        ? <String, dynamic>{'value': brightness.toString()}
+        ? <String, String>{'value': brightness.toString()}
         : <String, String>{},
     );
     if (result != null && result['value'] is String) {
@@ -765,9 +769,9 @@ class FlutterVmService {
     return null;
   }
 
-  Future<vm_service.Response> _checkedCallServiceExtension(
+  Future<vm_service.Response?> _checkedCallServiceExtension(
     String method, {
-    Map<String, dynamic> args,
+    Map<String, Object?>? args,
   }) async {
     try {
       return await service.callServiceExtension(method, args: args);
@@ -784,14 +788,14 @@ class FlutterVmService {
 
   /// Invoke a flutter extension method, if the flutter extension is not
   /// available, returns null.
-  Future<Map<String, dynamic>> invokeFlutterExtensionRpcRaw(
+  Future<Map<String, Object?>?> invokeFlutterExtensionRpcRaw(
     String method, {
-    @required String isolateId,
-    Map<String, dynamic> args,
+    required String isolateId,
+    Map<String, Object?>? args,
   }) async {
-    final vm_service.Response response = await _checkedCallServiceExtension(
+    final vm_service.Response? response = await _checkedCallServiceExtension(
       method,
-      args: <String, Object>{
+      args: <String, Object?>{
         'isolateId': isolateId,
         ...?args,
       },
@@ -810,7 +814,7 @@ class FlutterVmService {
     Duration delay = const Duration(milliseconds: 50),
   }) async {
     while (true) {
-      final vm_service.Response response = await callMethodWrapper(
+      final vm_service.Response? response = await callMethodWrapper(
         kListViewsMethod,
       );
       if (response == null) {
@@ -819,7 +823,7 @@ class FlutterVmService {
         // with cleaning up.
         return <FlutterView>[];
       }
-      final List<Object> rawViews = response.json['views'] as List<Object>;
+      final List<Object>? rawViews = response.json?['views'] as List<Object>?;
       final List<FlutterView> views = <FlutterView>[
         if (rawViews != null)
           for (final Object rawView in rawViews)
@@ -850,11 +854,11 @@ class FlutterVmService {
     }
 
     final Completer<vm_service.IsolateRef> extensionAdded = Completer<vm_service.IsolateRef>();
-    StreamSubscription<vm_service.Event> isolateEvents;
+    late final StreamSubscription<vm_service.Event> isolateEvents;
     isolateEvents = service.onIsolateEvent.listen((vm_service.Event event) {
       if (event.kind == vm_service.EventKind.kServiceExtensionAdded
           && event.extensionRPC == extensionName) {
-        isolateEvents?.cancel();
+        isolateEvents.cancel();
         extensionAdded.complete(event.isolate);
       }
     });
@@ -862,7 +866,7 @@ class FlutterVmService {
     try {
       final List<vm_service.IsolateRef> refs = await _getIsolateRefs();
       for (final vm_service.IsolateRef ref in refs) {
-        final vm_service.Isolate isolate = await getIsolateOrNull(ref.id);
+        final vm_service.Isolate? isolate = await getIsolateOrNull(ref.id!);
         if (isolate != null && isolate.extensionRPCs?.contains(extensionName) == true) {
           return ref;
         }
@@ -886,7 +890,7 @@ class FlutterVmService {
 
     final List<vm_service.IsolateRef> refs = <vm_service.IsolateRef>[];
     for (final FlutterView flutterView in flutterViews) {
-      final vm_service.IsolateRef uiIsolate = flutterView.uiIsolate;
+      final vm_service.IsolateRef? uiIsolate = flutterView.uiIsolate;
       if (uiIsolate != null) {
         refs.add(uiIsolate);
       }
@@ -896,11 +900,13 @@ class FlutterVmService {
 
   /// Attempt to retrieve the isolate with id [isolateId], or `null` if it has
   /// been collected.
-  Future<vm_service.Isolate> getIsolateOrNull(String isolateId) async {
+  Future<vm_service.Isolate?> getIsolateOrNull(String isolateId) async {
     return service.getIsolate(isolateId)
-      .catchError((dynamic error, StackTrace stackTrace) {
+      // The .then() call is required to cast from Future<Isolate> to Future<Isolate?>
+      .then<vm_service.Isolate?>((vm_service.Isolate isolate) => isolate)
+      .catchError((Object? error, StackTrace stackTrace) {
         return null;
-      }, test: (dynamic error) {
+      }, test: (Object? error) {
         return (error is vm_service.SentinelException) ||
           (error is vm_service.RPCError && error.code == RPCErrorCodes.kServiceDisappeared);
       });
@@ -912,7 +918,7 @@ class FlutterVmService {
     // has custom handling of certain RPCErrors.
     return service.callServiceExtension(
       '_createDevFS',
-      args: <String, dynamic>{'fsName': fsName},
+      args: <String, Object?>{'fsName': fsName},
     );
   }
 
@@ -920,15 +926,15 @@ class FlutterVmService {
   Future<void> deleteDevFS(String fsName) async {
     await _checkedCallServiceExtension(
       '_deleteDevFS',
-      args: <String, dynamic>{'fsName': fsName},
+      args: <String, Object?>{'fsName': fsName},
     );
   }
 
-  Future<vm_service.Response> screenshot() {
+  Future<vm_service.Response?> screenshot() {
     return _checkedCallServiceExtension(kScreenshotMethod);
   }
 
-  Future<vm_service.Response> screenshotSkp() {
+  Future<vm_service.Response?> screenshotSkp() {
     return _checkedCallServiceExtension(kScreenshotSkpMethod);
   }
 
@@ -937,13 +943,13 @@ class FlutterVmService {
     assert(recordedStreams != null);
     await _checkedCallServiceExtension(
       'setVMTimelineFlags',
-      args: <String, dynamic>{
+      args: <String, Object?>{
         'recordedStreams': recordedStreams,
       },
     );
   }
 
-  Future<vm_service.Response> getTimeline() {
+  Future<vm_service.Response?> getTimeline() {
     return _checkedCallServiceExtension('getVMTimeline');
   }
 
@@ -985,7 +991,7 @@ enum Brightness {
 
 /// Process a VM service log event into a string message.
 String processVmServiceMessage(vm_service.Event event) {
-  final String message = utf8.decode(base64.decode(event.bytes));
+  final String message = utf8.decode(base64.decode(event.bytes!));
   // Remove extra trailing newlines appended by the vm service.
   if (message.endsWith('\n')) {
     return message.substring(0, message.length - 1);
diff --git a/packages/flutter_tools/test/general.shard/device_test.dart b/packages/flutter_tools/test/general.shard/device_test.dart
index b2958fa6604..515db621d4e 100644
--- a/packages/flutter_tools/test/general.shard/device_test.dart
+++ b/packages/flutter_tools/test/general.shard/device_test.dart
@@ -481,7 +481,7 @@ void main() {
   });
 
   testWithoutContext('computeDartVmFlags handles various combinations of Dart VM flags and null_assertions', () {
-    expect(computeDartVmFlags(DebuggingOptions.enabled(BuildInfo.debug, dartFlags: null)), '');
+    expect(computeDartVmFlags(DebuggingOptions.enabled(BuildInfo.debug)), '');
     expect(computeDartVmFlags(DebuggingOptions.enabled(BuildInfo.debug, dartFlags: '--foo')), '--foo');
     expect(computeDartVmFlags(DebuggingOptions.enabled(BuildInfo.debug, dartFlags: '', nullAssertions: true)), '--null_assertions');
     expect(computeDartVmFlags(DebuggingOptions.enabled(BuildInfo.debug, dartFlags: '--foo', nullAssertions: true)), '--foo,--null_assertions');
diff --git a/packages/flutter_tools/test/general.shard/resident_runner_test.dart b/packages/flutter_tools/test/general.shard/resident_runner_test.dart
index dda956265b8..7eb912f232e 100644
--- a/packages/flutter_tools/test/general.shard/resident_runner_test.dart
+++ b/packages/flutter_tools/test/general.shard/resident_runner_test.dart
@@ -796,7 +796,7 @@ void main() {
         },
       ),
     ]);
-    final FakeDelegateFlutterDevice flutterDevice =  FakeDelegateFlutterDevice(
+    final FakeDelegateFlutterDevice flutterDevice = FakeDelegateFlutterDevice(
       device,
       BuildInfo.debug,
       FakeResidentCompiler(),
diff --git a/packages/flutter_tools/test/src/fake_vm_services.dart b/packages/flutter_tools/test/src/fake_vm_services.dart
index 299f3e18a18..b84ecf1d8ac 100644
--- a/packages/flutter_tools/test/src/fake_vm_services.dart
+++ b/packages/flutter_tools/test/src/fake_vm_services.dart
@@ -2,14 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
 import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/convert.dart';
 import 'package:flutter_tools/src/vmservice.dart';
-import 'package:meta/meta.dart';
 import 'package:test_api/test_api.dart' hide test; // ignore: deprecated_member_use
 import 'package:vm_service/vm_service.dart' as vm_service;
 
@@ -19,9 +16,9 @@ export 'package:test_api/test_api.dart' hide test, isInstanceOf; // ignore: depr
 /// and response structure.
 class FakeVmServiceHost {
   FakeVmServiceHost({
-    @required List<VmServiceExpectation> requests,
-    Uri httpAddress,
-    Uri wsAddress,
+    required List<VmServiceExpectation> requests,
+    Uri? httpAddress,
+    Uri? wsAddress,
   }) : _requests = requests {
     _vmService = FlutterVmService(vm_service.VmService(
       _input.stream,
@@ -44,16 +41,16 @@ class FakeVmServiceHost {
         return;
       }
       if (fakeRequest.errorCode == null) {
-        _input.add(json.encode(<String, Object>{
+        _input.add(json.encode(<String, Object?>{
           'jsonrpc': '2.0',
           'id': request['id'],
           'result': fakeRequest.jsonResponse ?? <String, Object>{'type': 'Success'},
         }));
       } else {
-        _input.add(json.encode(<String, Object>{
+        _input.add(json.encode(<String, Object?>{
           'jsonrpc': '2.0',
           'id': request['id'],
-          'error': <String, Object>{
+          'error': <String, Object?>{
             'code': fakeRequest.errorCode,
           }
         }));
@@ -67,7 +64,7 @@ class FakeVmServiceHost {
   final StreamController<String> _output = StreamController<String>();
 
   FlutterVmService get vmService => _vmService;
-  FlutterVmService _vmService;
+  late final FlutterVmService _vmService;
 
 
   bool get hasRemainingExpectations => _requests.isNotEmpty;
@@ -95,7 +92,7 @@ abstract class VmServiceExpectation {
 
 class FakeVmServiceRequest implements VmServiceExpectation {
   const FakeVmServiceRequest({
-    @required this.method,
+    required this.method,
     this.args = const <String, Object>{},
     this.jsonResponse,
     this.errorCode,
@@ -109,9 +106,9 @@ class FakeVmServiceRequest implements VmServiceExpectation {
 
   /// If non-null, the error code for a [vm_service.RPCError] in place of a
   /// standard response.
-  final int errorCode;
-  final Map<String, Object> args;
-  final Map<String, Object> jsonResponse;
+  final int? errorCode;
+  final Map<String, Object>? args;
+  final Map<String, Object>? jsonResponse;
 
   @override
   bool get isRequest => true;
@@ -119,8 +116,8 @@ class FakeVmServiceRequest implements VmServiceExpectation {
 
 class FakeVmServiceStreamResponse implements VmServiceExpectation {
   const FakeVmServiceStreamResponse({
-    @required this.event,
-    @required this.streamId,
+    required this.event,
+    required this.streamId,
   });
 
   final vm_service.Event event;