Migrate to null aware elements - Part 5 (flutter#172418)

## Description

Continuing the work from @jamilsaadeh97 to replace verbose null checks
with modern
[null_aware_elements](https://dart.dev/tools/linter-rules/use_null_aware_elements)
syntax.

This PR cleans up the remaining files not covered in the previous parts,
making the code more concise.

## Related PRs

- flutter#172198
- flutter#172306
- flutter#172307
- flutter#172322

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

Author: ricardodalarme

dev/bots/run_command.dart

@@ -212,7 +212,7 @@ Future<CommandResult> runCommand(
     }
     final String allOutput = '${result.flattenedStdout}\n${result.flattenedStderr}';
     foundError(<String>[
-      if (failureMessage != null) failureMessage,
+      ?failureMessage,
       '${bold}Command: $green$commandDescription$reset',
       if (failureMessage == null)
         '$bold${red}Command exited with exit code ${result.exitCode} but expected ${expectNonZeroExit ? (expectedExitCode ?? 'non-zero') : 'zero'} exit code.$reset',

dev/bots/utils.dart

@@ -458,7 +458,7 @@ Future<void> runDartTest(
     if (coverage != null) '--coverage=$coverage',
     if (perTestTimeout != null) '--timeout=${perTestTimeout.inMilliseconds}ms',
     if (runSkipped) '--run-skipped',
-    if (tags != null) ...tags.map((String t) => '--tags=$t'),
+    ...?tags?.map((String t) => '--tags=$t'),
     if (testPaths != null)
       for (final String testPath in testPaths) testPath,
   ];

dev/devicelab/lib/tasks/hot_mode_tests.dart

@@ -58,7 +58,7 @@ TaskFunction createHotModeTest({
       '--no-publish-port',
       '--verbose',
       '--uninstall-first',
-      if (additionalOptions != null) ...additionalOptions,
+      ...?additionalOptions,
     ];
     int hotReloadCount = 0;
     late Map<String, dynamic> smallReloadData;

dev/integration_tests/flutter_gallery/lib/demo/cupertino/cupertino_navigation_demo.dart

@@ -687,7 +687,7 @@ class Tab2ConversationRow extends StatelessWidget {
         mainAxisSize: MainAxisSize.min,
         crossAxisAlignment: isSelf ? CrossAxisAlignment.center : CrossAxisAlignment.end,
         children: <Widget>[
-          if (avatar != null) avatar!,
+          ?avatar,
           CupertinoUserInterfaceLevel(
             data: CupertinoUserInterfaceLevelData.elevated,
             child: Tab2ConversationBubble(

dev/integration_tests/flutter_gallery/lib/demo/shrine/home.dart

@@ -36,7 +36,7 @@ class HomePage extends StatelessWidget {
   Widget build(BuildContext context) {
     return Stack(
       children: <Widget>[
-        if (backdrop != null) backdrop!,
+        ?backdrop,
         Align(alignment: Alignment.bottomRight, child: expandingBottomSheet),
       ],
     );

dev/integration_tests/flutter_gallery/lib/gallery/home.dart

@@ -266,7 +266,7 @@ class _GalleryHomeState extends State<GalleryHome> with SingleTickerProviderStat
   static Widget _topHomeLayout(Widget? currentChild, List<Widget> previousChildren) {
     return Stack(
       alignment: Alignment.topCenter,
-      children: <Widget>[...previousChildren, if (currentChild != null) currentChild],
+      children: <Widget>[...previousChildren, ?currentChild],
     );
   }
 

dev/packages_autoroller/lib/src/repository.dart

@@ -299,12 +299,7 @@ abstract class Repository {
       }
       authorArg = '--author="$author"';
     }
-    final List<String> commitCmd = <String>[
-      'commit',
-      '--message',
-      message,
-      if (authorArg != null) authorArg,
-    ];
+    final List<String> commitCmd = <String>['commit', '--message', message, ?authorArg];
     stdio.printTrace('Executing git $commitCmd...');
     final io.ProcessResult commitResult = await git.run(
       commitCmd,

dev/tools/android_driver_extensions/lib/skia_gold.dart

@@ -158,6 +158,6 @@ final class _SkiaGoldComparator extends GoldenFileComparator {
       'Golden files in the Flutter framework must end with the file extension '
       '.png.',
     );
-    return Uri.parse(<String>[if (namePrefix != null) namePrefix!, golden.toString()].join('.'));
+    return Uri.parse(<String>[?namePrefix, golden.toString()].join('.'));
   }
 }

engine/src/flutter/lib/ui/text.dart

@@ -3526,10 +3526,7 @@ base class _NativeParagraphBuilder extends NativeFieldWrapperClass1 implements P
     final ByteData? encodedStrutStyle;
     if (strutStyle != null && strutStyle._enabled) {
       final String? fontFamily = strutStyle._fontFamily;
-      strutFontFamilies = <String>[
-        if (fontFamily != null) fontFamily,
-        ...?strutStyle._fontFamilyFallback,
-      ];
+      strutFontFamilies = <String>[?fontFamily, ...?strutStyle._fontFamilyFallback];
 
       assert(TextLeadingDistribution.values.length <= 2);
       final TextLeadingDistribution leadingDistribution =

examples/api/lib/widgets/slotted_render_object_widget/slotted_multi_child_render_object_widget_mixin.0.dart

@@ -87,10 +87,7 @@ class RenderDiagonal extends RenderBox
 
   // Returns children in hit test order.
   @override
-  Iterable<RenderBox> get children => <RenderBox>[
-    if (_topLeft != null) _topLeft!,
-    if (_bottomRight != null) _bottomRight!,
-  ];
+  Iterable<RenderBox> get children => <RenderBox>[?_topLeft, ?_bottomRight];
 
   // LAYOUT