diff --git a/pkg/front_end/test/crashing_test_case_minimizer_impl.dart b/pkg/front_end/test/crashing_test_case_minimizer_impl.dart
index e6ffb2bd9ef..8b716eb050d 100644
--- a/pkg/front_end/test/crashing_test_case_minimizer_impl.dart
+++ b/pkg/front_end/test/crashing_test_case_minimizer_impl.dart
@@ -290,7 +290,7 @@ class TestMinimizer {
 
     // For all dart files: Parse them as set their source as the parsed source
     // to "get around" any encoding issues when printing later.
-    Map<Uri, Uint8List> copy = new Map.from(_fs.data);
+    Map<Uri?, Uint8List?> copy = new Map.of(_fs.data);
     for (Uri? uri in _fs.data.keys) {
       if (await _shouldQuit()) break;
       String uriString = uri.toString();
@@ -726,7 +726,7 @@ class TestMinimizer {
 
     // TODO(jensj): don't use full uris.
     print("""
-# Copyright (c) 2021, the Dart project authors. Please see the AUTHORS file
+# Copyright (c) 2022, the Dart project authors. Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE.md file.
 
@@ -910,7 +910,7 @@ worlds:
     // Check if there now are any unused files.
     if (_latestComponent == null) return;
     Set<Uri> neededUris = _latestComponent!.uriToSource.keys.toSet();
-    Map<Uri, Uint8List> copy = new Map.from(_fs.data);
+    Map<Uri?, Uint8List?> copy = new Map.of(_fs.data);
     bool removedSome = false;
     if (await _shouldQuit()) return;
     for (MapEntry<Uri?, Uint8List?> entry in _fs.data.entries) {
@@ -947,7 +947,7 @@ worlds:
 
     if (!limitTo1) {
       if (await _shouldQuit()) return;
-      Map<Uri, Uint8List> copy = new Map.from(_fs.data);
+      Map<Uri?, Uint8List?> copy = new Map.of(_fs.data);
       // Try to remove content of i and the next 9 (10 files in total).
       for (int j = uriIndex; j < uriIndex + 10 && j < uris.length; j++) {
         Uri uri = uris[j];
@@ -1223,7 +1223,7 @@ worlds:
       // Try to load json and remove blocks.
       try {
         Map json = jsonDecode(utf8.decode(data));
-        Map jsonModified = new Map.from(json);
+        Map jsonModified = new Map.of(json);
         List packages = json["packages"];
         List packagesModified = new List.from(packages);
         jsonModified["packages"] = packagesModified;