diff --git a/dev/tools/gen_keycodes/lib/key_data.dart b/dev/tools/gen_keycodes/lib/key_data.dart
index a8d9994ac0..9dd567a32e 100644
--- a/dev/tools/gen_keycodes/lib/key_data.dart
+++ b/dev/tools/gen_keycodes/lib/key_data.dart
@@ -162,6 +162,7 @@ class KeyData {
       final String androidName = match.group(2);
       result[androidName] ??= <int>[];
       result[androidName].add(int.parse(match.group(1)));
+      return null;
     });
 
     return result;
@@ -178,9 +179,9 @@ class KeyData {
     headerFile = headerFile.replaceAllMapped(enumBlock, (Match match) => match.group(1));
     final RegExp enumEntry = RegExp(r'''AKEYCODE_([A-Z0-9_]+)\s*=\s*([0-9]+),?''');
     final Map<String, int> result = <String, int>{};
-    headerFile.replaceAllMapped(enumEntry, (Match match) {
+    for (Match match in enumEntry.allMatches(headerFile)) {
       result[match.group(1)] = int.parse(match.group(2));
-    });
+    }
     return result;
   }
 
@@ -193,9 +194,9 @@ class KeyData {
     // Only get the KEY definitions, ignore the rest (mouse, joystick, etc).
     final RegExp enumEntry = RegExp(r'''define GLFW_KEY_([A-Z0-9_]+)\s*([A-Z0-9_]+),?''');
     final Map<String, dynamic> replaced = <String, dynamic>{};
-    headerFile.replaceAllMapped(enumEntry, (Match match) {
+    for (Match match in enumEntry.allMatches(headerFile)) {
       replaced[match.group(1)] = int.tryParse(match.group(2)) ?? match.group(2).replaceAll('GLFW_KEY_', '');
-    });
+    }
     final Map<String, int> result = <String, int>{};
     replaced.forEach((String key, dynamic value) {
       // Some definition values point to other definitions (e.g #define GLFW_KEY_LAST GLFW_KEY_MENU).
diff --git a/packages/flutter_tools/lib/src/resident_runner.dart b/packages/flutter_tools/lib/src/resident_runner.dart
index 3c929a1607..c902802d31 100644
--- a/packages/flutter_tools/lib/src/resident_runner.dart
+++ b/packages/flutter_tools/lib/src/resident_runner.dart
@@ -182,7 +182,7 @@ class FlutterDevice {
     // The flutterExit message only returns if it fails, so just wait a few
     // seconds then assume it worked.
     // TODO(ianh): We should make this return once the VM service disconnects.
-    await Future.wait(futures).timeout(const Duration(seconds: 2), onTimeout: () { });
+    await Future.wait(futures).timeout(const Duration(seconds: 2), onTimeout: () => <void>[]);
   }
 
   Future<Uri> setupDevFS(
diff --git a/packages/flutter_tools/lib/src/run_hot.dart b/packages/flutter_tools/lib/src/run_hot.dart
index e59dcbb174..91339ca970 100644
--- a/packages/flutter_tools/lib/src/run_hot.dart
+++ b/packages/flutter_tools/lib/src/run_hot.dart
@@ -446,6 +446,7 @@ class HotRunner extends ResidentRunner {
                 // Resume the isolate so that it can be killed by the embedder.
                 return view.uiIsolate.resume();
               }
+              return null;
             },
           ).whenComplete(
             () { completer.complete(null); },
diff --git a/packages/flutter_tools/test/integration/test_driver.dart b/packages/flutter_tools/test/integration/test_driver.dart
index e7dacc5dc5..3f62692b36 100644
--- a/packages/flutter_tools/test/integration/test_driver.dart
+++ b/packages/flutter_tools/test/integration/test_driver.dart
@@ -366,6 +366,7 @@ abstract class FlutterTestDriver {
       _debugPrint('$task...');
       return callback()..timeout(timeout, onTimeout: () {
         _debugPrint('$task is taking longer than usual...');
+        return null;
       });
     }
 
@@ -388,6 +389,7 @@ abstract class FlutterTestDriver {
       print(messages.toString());
       timeoutExpired = true;
       print('$task is taking longer than usual...');
+      return null;
     });
 
     return future.catchError((dynamic error) {
diff --git a/packages/flutter_tools/test/ios/ios_workflow_test.dart b/packages/flutter_tools/test/ios/ios_workflow_test.dart
index eafaa192eb..6cd3401a13 100644
--- a/packages/flutter_tools/test/ios/ios_workflow_test.dart
+++ b/packages/flutter_tools/test/ios/ios_workflow_test.dart
@@ -187,6 +187,7 @@ Show information about a connected device.
   -x, --xml		output information as xml plist instead of key/value pairs
   -h, --help		prints usage information
         ''');
+        return null;
       });
       final IOSWorkflowTestTarget workflow = IOSWorkflowTestTarget();
       final ValidationResult result = await workflow.validate();