[flutter_tools] fix RangeError in gen-l10n by checking for empty string (#107604)

packages/flutter_tools/lib/src/localizations/gen_l10n.dart

@@ -1050,6 +1050,9 @@ class LocalizationsGenerator {
   }
 
   static bool _isValidGetterAndMethodName(String name) {
+    if (name.isEmpty) {
+      return false;
+    }
     // Public Dart method name must not start with an underscore
     if (name[0] == '_') {
       return false;

packages/flutter_tools/lib/src/localizations/gen_l10n_types.dart

@@ -124,6 +124,9 @@ class L10nException implements Exception {
   L10nException(this.message);
 
   final String message;
+
+  @override
+  String toString() => message;
 }
 
 // One optional named parameter to be used by a NumberFormat.

packages/flutter_tools/test/general.shard/generate_localizations_test.dart

@@ -992,9 +992,7 @@ class AppLocalizationsEn extends AppLocalizations {
     });
 
     testWithoutContext(
-      'throws an error attempting to add preferred locales '
-      'when there is no corresponding arb file for that '
-      'locale',
+      'throws an error attempting to add preferred locales when there is no corresponding arb file for that locale',
       () {
         final Directory l10nDirectory = fs.currentDirectory.childDirectory('lib').childDirectory('l10n')
           ..createSync(recursive: true);
@@ -1161,6 +1159,38 @@ class AppLocalizationsEn extends AppLocalizations {
         )),
       );
     });
+
+    testWithoutContext('throws when an empty string is used as a key', () {
+      const String arbFileStringWithEmptyResourceId = '''
+{
+  "market": "MARKET",
+  "": {
+    "description": "This key is invalid"
+  }
+}''';
+
+      final Directory l10nDirectory = fs.currentDirectory.childDirectory('lib').childDirectory('l10n')
+        ..createSync(recursive: true);
+      l10nDirectory.childFile('app_en.arb')
+        .writeAsStringSync(arbFileStringWithEmptyResourceId);
+
+      expect(
+        () => LocalizationsGenerator(
+          fileSystem: fs,
+          inputPathString: defaultL10nPathString,
+          outputPathString: defaultL10nPathString,
+          templateArbFileName: 'app_en.arb',
+          outputFileString: defaultOutputFileString,
+          classNameString: defaultClassNameString,
+        ).loadResources(),
+        throwsA(isA<L10nException>().having(
+          (L10nException e) => e.message,
+          'message',
+          contains('Invalid ARB resource name ""'),
+        )),
+      );
+    });
+
     testWithoutContext('throws when the same locale is detected more than once', () {
       const String secondMessageArbFileString = '''
 {