Prevent crashes due to missing or incomplete package_graph.json

Modify package graph parsing to safely handle missing package_graph.json file
and missing dependencies or devDependencies entries by using empty defaults
instead of throwing errors.

--- a/packages/flutter_tools/lib/src/package_graph.dart
+++ b/packages/flutter_tools/lib/src/package_graph.dart
@@ -36,18 +36,9 @@
     isExclusiveDevDependency: true,
   );

-  final List<String>? dependencies = packageGraph.dependencies[project.manifest.appName];
-  if (dependencies == null) {
-    throwToolExit('''
-Failed to parse ${packageGraph.file.path}: dependencies for `${project.manifest.appName}` missing.
-Try running `flutter pub get`''');
-  }
-  final List<String>? devDependencies = packageGraph.devDependencies[project.manifest.appName];
-  if (devDependencies == null) {
-    throwToolExit('''
-Failed to parse ${packageGraph.file.path}: devDependencies for `${project.manifest.appName}` missing.
-Try running `flutter pub get`''');
-  }
+  final List<String> dependencies = packageGraph.dependencies[project.manifest.appName] ?? <String>[];
+  final List<String> devDependencies = packageGraph.devDependencies[project.manifest.appName] ?? <String>[];
+
   final packageNamesToVisit = <String>[...dependencies, ...devDependencies];
   while (packageNamesToVisit.isNotEmpty) {
     final String current = packageNamesToVisit.removeLast();
@@ -55,13 +46,7 @@
       continue;
     }

-    final List<String>? dependencies = packageGraph.dependencies[current];
-
-    if (dependencies == null) {
-      throwToolExit('''
-Failed to parse ${packageGraph.file.path}: dependencies for `$current` missing.
-Try running `flutter pub get`''');
-    }
+    final List<String> dependencies = packageGraph.dependencies[current] ?? <String>[];
     packageNamesToVisit.addAll(dependencies);

     result[current] = Dependency(
@@ -89,7 +74,7 @@
       currentDependency.rootUri,
       isExclusiveDevDependency: false,
     );
-    packageNamesToVisit.addAll(packageGraph.dependencies[current]!);
+    packageNamesToVisit.addAll(packageGraph.dependencies[current] ?? <String>[]);
   }
   return result.values.toList();
 }
@@ -147,6 +132,9 @@
     final File file = project.packageConfig.fileSystem.file(
       project.packageConfig.uri.resolve('package_graph.json'),
     );
+    if (!file.existsSync()) {
+      return PackageGraph(file, <String>[], <String, List<String>>{}, <String, List<String>>{});
+    }
     try {
       return PackageGraph.fromJson(file, jsonDecode(file.readAsStringSync()));
     } on IOException catch (e) {

--- a/packages/flutter_tools/lib/src/isolated/native_assets/native_assets.dart
+++ b/packages/flutter_tools/lib/src/isolated/native_assets/native_assets.dart
@@ -384,7 +384,12 @@
 }

 Future<bool> _nativeBuildRequired(FlutterNativeAssetsBuildRunner buildRunner) async {
-  final List<String> packagesWithNativeAssets = await buildRunner.packagesWithNativeAssets();
+  late final List<String> packagesWithNativeAssets;
+  try {
+    packagesWithNativeAssets = await buildRunner.packagesWithNativeAssets();
+  } catch (error) {
+    packagesWithNativeAssets = <String>[];
+  }
   if (packagesWithNativeAssets.isEmpty) {
     globals.logger.printTrace(
       'No packages with native assets. Skipping native assets compilation.',
@@ -412,7 +417,12 @@
   FileSystem fileSystem,
   FlutterNativeAssetsBuildRunner buildRunner,
 ) async {
-  final List<String> packagesWithNativeAssets = await buildRunner.packagesWithNativeAssets();
+  late final List<String> packagesWithNativeAssets;
+  try {
+    packagesWithNativeAssets = await buildRunner.packagesWithNativeAssets();
+  } catch (error) {
+    packagesWithNativeAssets = <String>[];
+  }
   if (packagesWithNativeAssets.isEmpty) {
     globals.logger.printTrace(
       'No packages with native assets. Skipping native assets compilation.',