diff --git a/samples/sample_extension/sample_asynchronous_extension.dart b/samples/sample_extension/sample_asynchronous_extension.dart
index 541652dde5a..7d189022e8c 100644
--- a/samples/sample_extension/sample_asynchronous_extension.dart
+++ b/samples/sample_extension/sample_asynchronous_extension.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 library sample_asynchronous_extension;
 
 import 'dart:async';
@@ -12,15 +10,12 @@ import 'dart-ext:sample_extension';
 
 // A class caches the native port used to call an asynchronous extension.
 class RandomArray {
-  static SendPort _port;
+  static SendPort? _port;
 
   Future<List<int>> randomArray(int seed, int length) {
     var completer = new Completer<List<int>>();
     var replyPort = new RawReceivePort();
-    var args = new List(3);
-    args[0] = seed;
-    args[1] = length;
-    args[2] = replyPort.sendPort;
+    var args = [seed, length, replyPort.sendPort];
     _servicePort.send(args);
     replyPort.handler = (result) {
       replyPort.close();
@@ -37,7 +32,7 @@ class RandomArray {
     if (_port == null) {
       _port = _newServicePort();
     }
-    return _port;
+    return _port!;
   }
 
   SendPort _newServicePort() native "RandomArray_ServicePort";
diff --git a/samples/sample_extension/sample_synchronous_extension.dart b/samples/sample_extension/sample_synchronous_extension.dart
index e5ad660a79f..727cd4cf598 100644
--- a/samples/sample_extension/sample_synchronous_extension.dart
+++ b/samples/sample_extension/sample_synchronous_extension.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 library sample_synchronous_extension;
 
 import 'dart-ext:sample_extension';
diff --git a/samples/sample_extension/test/sample_extension_app_snapshot_test.dart b/samples/sample_extension/test/sample_extension_app_snapshot_test.dart
index b2eb2041eb7..558b108fd8d 100644
--- a/samples/sample_extension/test/sample_extension_app_snapshot_test.dart
+++ b/samples/sample_extension/test/sample_extension_app_snapshot_test.dart
@@ -4,8 +4,6 @@
 //
 // Dart test program for testing native extensions.
 
-// @dart = 2.9
-
 // OtherResources=../sample_synchronous_extension.dart
 // OtherResources=../sample_asynchronous_extension.dart
 // OtherResources=../test_sample_synchronous_extension.dart
diff --git a/samples/sample_extension/test/sample_extension_test.dart b/samples/sample_extension/test/sample_extension_test.dart
index 393463bfb6d..4311ff544f7 100644
--- a/samples/sample_extension/test/sample_extension_test.dart
+++ b/samples/sample_extension/test/sample_extension_test.dart
@@ -4,8 +4,6 @@
 //
 // Dart test program for testing native extensions.
 
-// @dart = 2.9
-
 import 'sample_extension_test_helper.dart';
 
 void main() {
diff --git a/samples/sample_extension/test/sample_extension_test_helper.dart b/samples/sample_extension/test/sample_extension_test_helper.dart
index 9c701bf3f84..d4cae3da4b5 100644
--- a/samples/sample_extension/test/sample_extension_test_helper.dart
+++ b/samples/sample_extension/test/sample_extension_test_helper.dart
@@ -4,8 +4,6 @@
 //
 // Dart test program for testing native extensions.
 
-// @dart = 2.9
-
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
@@ -26,7 +24,7 @@ Future copyFileToDirectory(String file, String directory) async {
       result = await Process.run('cmd.exe', ['/C', 'copy $src $dst']);
       break;
     default:
-      Expect.fail('Unknown operating system ${Platform.operatingSystem}');
+      throw 'Unknown operating system ${Platform.operatingSystem}';
   }
   if (result.exitCode != 0) {
     print(result.stdout);
@@ -46,7 +44,7 @@ Future run(String program, List<String> arguments) async {
   }
 }
 
-Future testNativeExtensions(String snapshotKind) async {
+Future testNativeExtensions(String? snapshotKind) async {
   String buildDirectory = dirname(Platform.executable);
   Directory tempDirectory =
       Directory.systemTemp.createTempSync('sample_extension_');
diff --git a/samples/sample_extension/test_sample_asynchronous_extension.dart b/samples/sample_extension/test_sample_asynchronous_extension.dart
index 5ceb7c80753..b1fd41933d9 100644
--- a/samples/sample_extension/test_sample_asynchronous_extension.dart
+++ b/samples/sample_extension/test_sample_asynchronous_extension.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 library test_sample_extension;
 
 import 'sample_asynchronous_extension.dart';
@@ -32,16 +30,16 @@ void main() {
 void checkNormal(List l) {
   // Count how many times each byte value occurs.  Assert that the counts
   // are all within a reasonable (six-sigma) range.
-  List counts = new List<int>.filled(256, 0);
+  List<int> counts = new List<int>.filled(256, 0);
   for (var e in l) {
     counts[e]++;
   }
   new RandomArray().randomArray(18, 256000).then(checkCorrelation(counts));
 }
 
-Function checkCorrelation(List counts) {
-  return (List l) {
-    List counts_2 = new List<int>.filled(256, 0);
+dynamic Function(List<int>) checkCorrelation(List<int> counts) {
+  return (List<int> l) {
+    List<int> counts_2 = new List<int>.filled(256, 0);
     for (var e in l) {
       counts_2[e]++;
     }
diff --git a/samples/sample_extension/test_sample_synchronous_extension.dart b/samples/sample_extension/test_sample_synchronous_extension.dart
index 77d2fc337e3..ac177245cea 100644
--- a/samples/sample_extension/test_sample_synchronous_extension.dart
+++ b/samples/sample_extension/test_sample_synchronous_extension.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 library test_sample_extension;
 
 import 'sample_synchronous_extension.dart';