diff --git a/packages/flutter_goldens/lib/flutter_goldens.dart b/packages/flutter_goldens/lib/flutter_goldens.dart
index 739d6d94bc..c6b63eecb9 100644
--- a/packages/flutter_goldens/lib/flutter_goldens.dart
+++ b/packages/flutter_goldens/lib/flutter_goldens.dart
@@ -103,10 +103,7 @@ abstract class FlutterGoldenFileComparator extends GoldenFileComparator {
     this.skiaClient, {
     this.fs = const LocalFileSystem(),
     this.platform = const LocalPlatform(),
-  }) : assert(basedir != null),
-       assert(skiaClient != null),
-       assert(fs != null),
-       assert(platform != null);
+  });
 
   /// The directory to which golden file URIs will be resolved in [compare] and
   /// [update], cannot be null.
@@ -132,7 +129,7 @@ abstract class FlutterGoldenFileComparator extends GoldenFileComparator {
   }
 
   @override
-  Uri getTestUri(Uri key, int version) => key;
+  Uri getTestUri(Uri key, int? version) => key;
 
   /// Calculate the appropriate basedir for the current test context.
   ///
@@ -231,8 +228,8 @@ class FlutterPostSubmitFileComparator extends FlutterGoldenFileComparator {
   /// purposes only.
   static Future<FlutterPostSubmitFileComparator> fromDefaultComparator(
     final Platform platform, {
-    SkiaGoldClient goldens,
-    LocalFileComparator defaultComparator,
+    SkiaGoldClient? goldens,
+    LocalFileComparator? defaultComparator,
   }) async {
 
     defaultComparator ??= goldenFileComparator as LocalFileComparator;
@@ -326,9 +323,9 @@ class FlutterPreSubmitFileComparator extends FlutterGoldenFileComparator {
   /// purposes only.
   static Future<FlutterGoldenFileComparator> fromDefaultComparator(
     final Platform platform, {
-    SkiaGoldClient goldens,
-    LocalFileComparator defaultComparator,
-    final Directory testBasedir,
+    SkiaGoldClient? goldens,
+    LocalFileComparator? defaultComparator,
+    Directory? testBasedir,
   }) async {
 
     defaultComparator ??= goldenFileComparator as LocalFileComparator;
@@ -353,7 +350,7 @@ class FlutterPreSubmitFileComparator extends FlutterGoldenFileComparator {
       // Some contributors may not have permission on Cirrus to decrypt the
       // service account.
       onCirrusWithPermission =
-        !platform.environment['GOLD_SERVICE_ACCOUNT'].startsWith('ENCRYPTED');
+        !platform.environment['GOLD_SERVICE_ACCOUNT']!.startsWith('ENCRYPTED');
     }
     final bool onLuci = platform.environment.containsKey('SWARMING_TASK_ID');
     if (onCirrusWithPermission || onLuci) {
@@ -457,7 +454,7 @@ class _UnauthorizedFlutterPreSubmitComparator extends FlutterPreSubmitFileCompar
     // low.
     skiaClient.getExpectations();
     final String testName = skiaClient.cleanTestName(golden.path);
-    final List<String> testExpectations = skiaClient.expectations[testName];
+    final List<String>? testExpectations = skiaClient.expectations[testName];
     if (testExpectations == null) {
       // This is a new test.
       print('No expectations provided by Skia Gold for test: $golden. '
@@ -502,8 +499,7 @@ class FlutterSkippingFileComparator extends FlutterGoldenFileComparator {
     final Uri basedir,
     final SkiaGoldClient skiaClient,
     this.reason,
-  ) : assert(reason != null),
-      super(basedir, skiaClient);
+  ) : super(basedir, skiaClient);
 
   /// Describes the reason for using the [FlutterSkippingFileComparator].
   ///
@@ -514,12 +510,12 @@ class FlutterSkippingFileComparator extends FlutterGoldenFileComparator {
   /// relative path resolution of the default [goldenFileComparator].
   static FlutterSkippingFileComparator fromDefaultComparator(
     String reason, {
-    LocalFileComparator defaultComparator,
+    LocalFileComparator? defaultComparator,
   }) {
     defaultComparator ??= goldenFileComparator as LocalFileComparator;
     const FileSystem fs = LocalFileSystem();
     final Uri basedir = defaultComparator.basedir;
-    final SkiaGoldClient skiaClient = SkiaGoldClient(fs.directory(basedir));
+    final SkiaGoldClient skiaClient = SkiaGoldClient(fs.directory(basedir), ci: ContinuousIntegrationEnvironment.none);
     return FlutterSkippingFileComparator(basedir, skiaClient, reason);
   }
 
@@ -532,7 +528,7 @@ class FlutterSkippingFileComparator extends FlutterGoldenFileComparator {
   }
 
   @override
-  Future<void> update(Uri golden, Uint8List imageBytes) => null;
+  Future<void> update(Uri golden, Uint8List imageBytes) async {}
 
   /// Decides, based on the current environment, if this comparator should be
   /// used.
@@ -596,9 +592,9 @@ class FlutterLocalFileComparator extends FlutterGoldenFileComparator with LocalC
   /// visible for testing purposes only.
   static Future<FlutterGoldenFileComparator> fromDefaultComparator(
     final Platform platform, {
-    SkiaGoldClient goldens,
-    LocalFileComparator defaultComparator,
-    Directory baseDirectory,
+    SkiaGoldClient? goldens,
+    LocalFileComparator? defaultComparator,
+    Directory? baseDirectory,
   }) async {
     defaultComparator ??= goldenFileComparator as LocalFileComparator;
     baseDirectory ??= FlutterGoldenFileComparator.getBaseDirectory(
@@ -611,7 +607,7 @@ class FlutterLocalFileComparator extends FlutterGoldenFileComparator with LocalC
       baseDirectory.createSync(recursive: true);
     }
 
-    goldens ??= SkiaGoldClient(baseDirectory);
+    goldens ??= SkiaGoldClient(baseDirectory, ci: ContinuousIntegrationEnvironment.none);
 
     try {
       await goldens.getExpectations();
@@ -638,7 +634,7 @@ class FlutterLocalFileComparator extends FlutterGoldenFileComparator with LocalC
   Future<bool> compare(Uint8List imageBytes, Uri golden) async {
     golden = _addPrefix(golden);
     final String testName = skiaClient.cleanTestName(golden.path);
-    final List<String> testExpectations = skiaClient.expectations[testName];
+    final List<String>? testExpectations = skiaClient.expectations[testName];
     if (testExpectations == null) {
       // There is no baseline for this test
       print('No expectations provided by Skia Gold for test: $golden. '
diff --git a/packages/flutter_goldens/pubspec.yaml b/packages/flutter_goldens/pubspec.yaml
index 351cb09393..7abdec0dad 100644
--- a/packages/flutter_goldens/pubspec.yaml
+++ b/packages/flutter_goldens/pubspec.yaml
@@ -2,7 +2,7 @@ name: flutter_goldens
 
 environment:
   # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.0.0-dev.68.0 <3.0.0"
+  sdk: ">=2.10.0-4.0.dev <2.10.0"
 
 dependencies:
   # To update these, use "flutter update-packages --force-upgrade".
diff --git a/packages/flutter_goldens/test/flutter_goldens_test.dart b/packages/flutter_goldens/test/flutter_goldens_test.dart
index 5045a095b3..1177b87767 100644
--- a/packages/flutter_goldens/test/flutter_goldens_test.dart
+++ b/packages/flutter_goldens/test/flutter_goldens_test.dart
@@ -2,6 +2,7 @@
 // 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:convert';
 import 'dart:core';
@@ -75,6 +76,7 @@ void main() {
         process: process,
         platform: platform,
         httpClient: mockHttpClient,
+        ci: ContinuousIntegrationEnvironment.luci,
       );
     });
 
@@ -148,6 +150,7 @@ void main() {
         process: process,
         platform: platform,
         httpClient: mockHttpClient,
+        ci: ContinuousIntegrationEnvironment.luci
       );
 
       when(process.run(
diff --git a/packages/flutter_goldens_client/lib/skia_client.dart b/packages/flutter_goldens_client/lib/skia_client.dart
index 0710eeb7e5..251707c25b 100644
--- a/packages/flutter_goldens_client/lib/skia_client.dart
+++ b/packages/flutter_goldens_client/lib/skia_client.dart
@@ -25,6 +25,7 @@ const String _kTestBrowserKey = 'FLUTTER_TEST_BROWSER';
 enum ContinuousIntegrationEnvironment {
   luci,
   cirrus,
+  none,
 }
 
 /// A client for uploading image tests and making baseline requests to the
@@ -35,13 +36,9 @@ class SkiaGoldClient {
     this.fs = const LocalFileSystem(),
     this.process = const LocalProcessManager(),
     this.platform = const LocalPlatform(),
-    this.ci,
-    io.HttpClient httpClient,
-  }) : assert(workDirectory != null),
-       assert(fs != null),
-       assert(process != null),
-       assert(platform != null),
-       httpClient = httpClient ?? io.HttpClient();
+    required this.ci,
+    io.HttpClient? httpClient,
+  }) : httpClient = httpClient ?? io.HttpClient();
 
   /// The file system to use for storing the local clone of the repository.
   ///
@@ -83,7 +80,7 @@ class SkiaGoldClient {
   /// [_UnauthorizedFlutterPreSubmitComparator] to test against golden masters
   /// maintained in the Flutter Gold dashboard.
   Map<String, List<String>> get expectations => _expectations;
-  Map<String, List<String>> _expectations;
+  late Map<String, List<String>> _expectations;
 
   /// The local [Directory] where the Flutter repository is hosted.
   ///
@@ -93,13 +90,13 @@ class SkiaGoldClient {
   /// The path to the local [Directory] where the goldctl tool is hosted.
   ///
   /// Uses the [platform] environment in this implementation.
-  String/*!*/ get _goldctl => platform.environment[_kGoldctlKey];
+  String get _goldctl => platform.environment[_kGoldctlKey]!;
 
   /// The path to the local [Directory] where the service account key is
   /// hosted.
   ///
   /// Uses the [platform] environment in this implementation.
-  String/*!*/ get _serviceAccount => platform.environment[_kServiceAccountKey];
+  String get _serviceAccount => platform.environment[_kServiceAccountKey]!;
 
   /// Prepares the local work space for golden file testing and calls the
   /// goldctl `auth` command.
@@ -116,9 +113,9 @@ class SkiaGoldClient {
       return;
 
     List<String> authArguments;
-    /*late*/ String failureContext;
+    String failureContext;
 
-    switch (ci/*!*/) {
+    switch (ci) {
       case ContinuousIntegrationEnvironment.luci:
         authArguments = <String>[
           'auth',
@@ -154,6 +151,8 @@ class SkiaGoldClient {
           'Cirrus, if the debug information below contains ENCRYPTED, the wrong '
           'comparator was chosen for the test case.';
         break;
+      case ContinuousIntegrationEnvironment.none:
+        return;
     }
 
     final io.ProcessResult result = await io.Process.run(
@@ -267,9 +266,6 @@ class SkiaGoldClient {
   /// The [testName] and [goldenFile] parameters reference the current
   /// comparison being evaluated by the [FlutterPostSubmitFileComparator].
   Future<bool> imgtestAdd(String testName, File goldenFile) async {
-    assert(testName != null);
-    assert(goldenFile != null);
-
     final List<String> imgtestArguments = <String>[
       'imgtest', 'add',
       '--work-dir', workDirectory
@@ -361,9 +357,6 @@ class SkiaGoldClient {
   /// The [testName] and [goldenFile] parameters reference the current
   /// comparison being evaluated by the [_AuthorizedFlutterPreSubmitComparator].
   Future<void> tryjobAdd(String testName, File goldenFile) async {
-    assert(testName != null);
-    assert(goldenFile != null);
-
     final List<String> imgtestArguments = <String>[
       'imgtest', 'add',
       '--work-dir', workDirectory
@@ -410,9 +403,6 @@ class SkiaGoldClient {
   /// comparison being evaluated by the
   /// [_UnauthorizedFlutterPreSubmitComparator].
   Future<bool> imgtestCheck(String testName, File goldenFile) async {
-    assert(testName != null);
-    assert(goldenFile != null);
-
     final List<String> imgtestArguments = <String>[
       'imgtest', 'check',
       '--work-dir', workDirectory
@@ -440,7 +430,7 @@ class SkiaGoldClient {
       );
       const String mainKey = 'master';
       const String temporaryKey = 'master_str';
-      String rawResponse;
+      late String rawResponse;
       try {
         final io.HttpClientRequest request = await httpClient.getUrl(requestForExpectations);
         final io.HttpClientResponse response = await request.close();
@@ -448,7 +438,7 @@ class SkiaGoldClient {
         final dynamic jsonResponse = json.decode(rawResponse);
         if (jsonResponse is! Map<String, dynamic>)
           throw const FormatException('Skia gold expectations do not match expected format.');
-        final Map<String, dynamic> skiaJson = (jsonResponse[mainKey] ?? jsonResponse[temporaryKey]) as Map<String, dynamic>;
+        final Map<String, dynamic>? skiaJson = (jsonResponse[mainKey] ?? jsonResponse[temporaryKey]) as Map<String, dynamic>?;
         if (skiaJson == null)
           throw FormatException('Skia gold expectations are missing the "$mainKey" key (and also doesn\'t have "$temporaryKey")! Available keys: ${jsonResponse.keys.join(", ")}');
         skiaJson.forEach((String key, dynamic value) {
@@ -506,7 +496,7 @@ class SkiaGoldClient {
   Future<bool> testIsIgnoredForPullRequest(String pullRequest, String testName) async {
     bool ignoreIsActive = false;
     testName = cleanTestName(testName);
-    String rawResponse;
+    late String rawResponse;
     await io.HttpOverrides.runWithHttpOverrides<Future<void>>(() async {
       final Uri requestForIgnores = Uri.parse(
         'https://flutter-gold.skia.org/json/ignores'
@@ -565,7 +555,7 @@ class SkiaGoldClient {
   Future<bool> isValidDigestForExpectation(String expectation, String testName) async {
     bool isValid = false;
     testName = cleanTestName(testName);
-    String rawResponse;
+    late String rawResponse;
     await io.HttpOverrides.runWithHttpOverrides<Future<void>>(() async {
       final Uri requestForDigest = Uri.parse(
         'https://flutter-gold.skia.org/json/details?test=$testName&digest=$expectation'
@@ -653,22 +643,24 @@ class SkiaGoldClient {
   /// Returns a list of arguments for initializing a tryjob based on the testing
   /// environment.
   List<String> getCIArguments() {
-    /*late*/ String/*!*/ pullRequest;
-    /*late*/ String/*!*/ jobId;
-    /*late*/ String cis;
+    String pullRequest;
+    String jobId;
+    String cis;
 
-    switch (ci/*!*/) {
+    switch (ci) {
       case ContinuousIntegrationEnvironment.luci:
-        jobId = platform.environment['LOGDOG_STREAM_PREFIX'].split('/').last;
-        final List<String> refs = platform.environment['GOLD_TRYJOB'].split('/');
+        jobId = platform.environment['LOGDOG_STREAM_PREFIX']!.split('/').last;
+        final List<String> refs = platform.environment['GOLD_TRYJOB']!.split('/');
         pullRequest = refs[refs.length - 2];
         cis = 'buildbucket';
         break;
       case ContinuousIntegrationEnvironment.cirrus:
-        pullRequest = platform.environment['CIRRUS_PR'];
-        jobId = platform.environment['CIRRUS_TASK_ID'];
+        pullRequest = platform.environment['CIRRUS_PR']!;
+        jobId = platform.environment['CIRRUS_TASK_ID']!;
         cis = 'cirrus';
         break;
+      case ContinuousIntegrationEnvironment.none:
+        return <String>[];
     }
 
     return <String>[
@@ -685,17 +677,17 @@ class SkiaGoldHttpOverrides extends io.HttpOverrides {}
 /// A digest returned from a request to the Flutter Gold dashboard.
 class SkiaGoldDigest {
   const SkiaGoldDigest({
-    this.imageHash,
-    this.paramSet,
-    this.testName,
-    this.status,
+    required this.imageHash,
+    required this.paramSet,
+    required this.testName,
+    required this.status,
   });
 
   /// Create a digest from requested JSON.
   factory SkiaGoldDigest.fromJson(Map<String, dynamic> json) {
     return SkiaGoldDigest(
       imageHash: json['digest'] as String,
-      paramSet: Map<String, dynamic>.from(json['paramset'] as Map<String, dynamic> ??
+      paramSet: Map<String, dynamic>.from(json['paramset'] as Map<String, dynamic>? ??
         <String, List<String>>{
           'Platform': <String>[],
           'Browser' : <String>[],
@@ -706,16 +698,16 @@ class SkiaGoldDigest {
   }
 
   /// Unique identifier for the image associated with the digest.
-  final String/*!*/ imageHash;
+  final String imageHash;
 
   /// Parameter set for the given test, e.g. Platform : Windows.
-  final Map<String, dynamic>/*!*/ paramSet;
+  final Map<String, dynamic> paramSet;
 
   /// Test name associated with the digest, e.g. positive or un-triaged.
-  final String/*!*/ testName;
+  final String testName;
 
   /// Status of the given digest, e.g. positive or un-triaged.
-  final String/*!*/ status;
+  final String status;
 
   /// Validates a given digest against the current testing conditions.
   bool isValid(Platform platform, String name, String expectation) {
diff --git a/packages/flutter_goldens_client/pubspec.yaml b/packages/flutter_goldens_client/pubspec.yaml
index 872aaaf397..32bc7f97f3 100644
--- a/packages/flutter_goldens_client/pubspec.yaml
+++ b/packages/flutter_goldens_client/pubspec.yaml
@@ -2,7 +2,7 @@ name: flutter_goldens_client
 
 environment:
   # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.0.0-dev.68.0 <3.0.0"
+  sdk: ">=2.10.0-4.0.dev <2.10.0 <3.0.0"
 
 dependencies:
   # To update these, use "flutter update-packages --force-upgrade".
diff --git a/packages/flutter_test/lib/src/_goldens_io.dart b/packages/flutter_test/lib/src/_goldens_io.dart
index 5db2baf25a..531fead90b 100644
--- a/packages/flutter_test/lib/src/_goldens_io.dart
+++ b/packages/flutter_test/lib/src/_goldens_io.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.10
 import 'dart:async';
 import 'dart:io';
 import 'dart:math' as math;
@@ -61,15 +62,15 @@ class LocalFileComparator extends GoldenFileComparator with LocalComparisonOutpu
   /// directory in which [testFile] resides.
   ///
   /// The [testFile] URL must represent a file.
-  LocalFileComparator(Uri testFile, {path.Style pathStyle})
+  LocalFileComparator(Uri testFile, {path.Style? pathStyle})
     : basedir = _getBasedir(testFile, pathStyle),
       _path = _getPath(pathStyle);
 
-  static path.Context _getPath(path.Style style) {
+  static path.Context _getPath(path.Style? style) {
     return path.Context(style: style ?? path.Style.platform);
   }
 
-  static Uri _getBasedir(Uri testFile, path.Style pathStyle) {
+  static Uri _getBasedir(Uri testFile, path.Style? pathStyle) {
     final path.Context context = _getPath(pathStyle);
     final String testFilePath = context.fromUri(testFile);
     final String testDirectoryPath = context.dirname(testFilePath);
@@ -135,7 +136,7 @@ class LocalComparisonOutput {
     if (result.diffs != null) {
       additionalFeedback = '\nFailure feedback can be found at '
         '${path.join(basedir.path, 'failures')}';
-      final Map<String, Image> diffs = result.diffs.cast<String, Image>();
+      final Map<String, Image> diffs = result.diffs!.cast<String, Image>();
       for (final MapEntry<String, Image> entry in diffs.entries) {
         final File output = getFailureFile(
           key.isEmpty ? entry.key : entry.key + '_' + key,
@@ -143,9 +144,9 @@ class LocalComparisonOutput {
           basedir,
         );
         output.parent.createSync(recursive: true);
-        final ByteData pngBytes =
+        final ByteData? pngBytes =
             await entry.value.toByteData(format: ImageByteFormat.png);
-        output.writeAsBytesSync(pngBytes.buffer.asUint8List());
+        output.writeAsBytesSync(pngBytes!.buffer.asUint8List());
       }
     }
     throw test_package.TestFailure(
@@ -169,7 +170,7 @@ class LocalComparisonOutput {
 
 /// Returns a [ComparisonResult] to describe the pixel differential of the
 /// [test] and [master] image bytes provided.
-Future<ComparisonResult> compareLists(List<int> test, List<int> master) async {
+Future<ComparisonResult> compareLists(List<int>? test, List<int>? master) async {
   if (identical(test, master))
     return ComparisonResult(passed: true);
 
@@ -183,15 +184,12 @@ Future<ComparisonResult> compareLists(List<int> test, List<int> master) async {
   final Codec testImageCodec =
       await instantiateImageCodec(Uint8List.fromList(test));
   final Image testImage = (await testImageCodec.getNextFrame()).image;
-  final ByteData testImageRgba = await testImage.toByteData();
+  final ByteData? testImageRgba = await testImage.toByteData();
 
   final Codec masterImageCodec =
       await instantiateImageCodec(Uint8List.fromList(master));
   final Image masterImage = (await masterImageCodec.getNextFrame()).image;
-  final ByteData masterImageRgba = await masterImage.toByteData();
-
-  assert(testImage != null);
-  assert(masterImage != null);
+  final ByteData? masterImageRgba = await masterImage.toByteData();
 
   final int width = testImage.width;
   final int height = testImage.height;
@@ -207,10 +205,10 @@ Future<ComparisonResult> compareLists(List<int> test, List<int> master) async {
 
   int pixelDiffCount = 0;
   final int totalPixels = width * height;
-  final ByteData invertedMasterRgba = _invert(masterImageRgba);
-  final ByteData invertedTestRgba = _invert(testImageRgba);
+  final ByteData invertedMasterRgba = _invert(masterImageRgba!);
+  final ByteData invertedTestRgba = _invert(testImageRgba!);
 
-  final Uint8List testImageBytes = (await testImage.toByteData()).buffer.asUint8List();
+  final Uint8List testImageBytes = (await testImage.toByteData())!.buffer.asUint8List();
   final ByteData maskedDiffRgba = ByteData(testImageBytes.length);
   maskedDiffRgba.buffer.asUint8List().setRange(0, testImageBytes.length, testImageBytes);
   final ByteData isolatedDiffRgba = ByteData(width * height * 4);
diff --git a/packages/flutter_test/lib/src/_goldens_web.dart b/packages/flutter_test/lib/src/_goldens_web.dart
index 75c0931331..68dc03e6ab 100644
--- a/packages/flutter_test/lib/src/_goldens_web.dart
+++ b/packages/flutter_test/lib/src/_goldens_web.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.10
 import 'dart:convert';
 import 'dart:html' as html;
 import 'dart:typed_data';
diff --git a/packages/flutter_test/lib/src/goldens.dart b/packages/flutter_test/lib/src/goldens.dart
index 26af731cbe..3f83f14f45 100644
--- a/packages/flutter_test/lib/src/goldens.dart
+++ b/packages/flutter_test/lib/src/goldens.dart
@@ -2,10 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.10
 import 'dart:async';
 import 'dart:typed_data';
 
-import 'package:meta/meta.dart';
 import 'package:path/path.dart' as path;
 import '_goldens_io.dart' if (dart.library.html) '_goldens_web.dart' as _goldens;
 
@@ -82,7 +82,7 @@ abstract class GoldenFileComparator {
   ///
   /// Version numbers are used in golden file tests for package:flutter. You can
   /// learn more about these tests [here](https://github.com/flutter/flutter/wiki/Writing-a-golden-file-test-for-package:flutter).
-  Uri getTestUri(Uri key, int version) {
+  Uri getTestUri(Uri key, int? version) {
     if (version == null)
       return key;
     final String keyString = key.toString();
@@ -130,7 +130,6 @@ abstract class GoldenFileComparator {
 GoldenFileComparator get goldenFileComparator => _goldenFileComparator;
 GoldenFileComparator _goldenFileComparator = const TrivialComparator._();
 set goldenFileComparator(GoldenFileComparator value) {
-  assert(value != null);
   _goldenFileComparator = value;
 }
 
@@ -194,7 +193,7 @@ abstract class WebGoldenComparator {
   ///
   /// Version numbers are used in golden file tests for package:flutter. You can
   /// learn more about these tests [here](https://github.com/flutter/flutter/wiki/Writing-a-golden-file-test-for-package:flutter).
-  Uri getTestUri(Uri key, int version) {
+  Uri getTestUri(Uri key, int? version) {
     if (version == null)
       return key;
     final String keyString = key.toString();
@@ -239,7 +238,6 @@ abstract class WebGoldenComparator {
 WebGoldenComparator get webGoldenComparator => _webGoldenComparator;
 WebGoldenComparator _webGoldenComparator = const _TrivialWebGoldenComparator._();
 set webGoldenComparator(WebGoldenComparator value) {
-  assert(value != null);
   _webGoldenComparator = value;
 }
 
@@ -289,7 +287,7 @@ class TrivialComparator implements GoldenFileComparator {
   }
 
   @override
-  Uri getTestUri(Uri key, int version) {
+  Uri getTestUri(Uri key, int? version) {
     return key;
   }
 }
@@ -309,7 +307,7 @@ class _TrivialWebGoldenComparator implements WebGoldenComparator {
   }
 
   @override
-  Uri getTestUri(Uri key, int version) {
+  Uri getTestUri(Uri key, int? version) {
     return key;
   }
 }
@@ -322,10 +320,10 @@ class _TrivialWebGoldenComparator implements WebGoldenComparator {
 class ComparisonResult {
   /// Creates a new [ComparisonResult] for the current test.
   ComparisonResult({
-    @required this.passed,
+    required this.passed,
     this.error,
     this.diffs,
-  }) : assert(passed != null);
+  });
 
   /// Indicates whether or not a pixel comparison test has failed.
   ///
@@ -333,10 +331,10 @@ class ComparisonResult {
   final bool passed;
 
   /// Error message used to describe the cause of the pixel comparison failure.
-  final String error;
+  final String? error;
 
   /// Map containing differential images to illustrate found variants in pixel
   /// values in the execution of the pixel test.
   // TODO(jonahwilliams): fix type signature when image is updated to support web.
-  final Map<String, Object> diffs;
+  final Map<String, Object>? diffs;
 }