Resolved contradictory documentation of showGeneralDialog and default value of...

Resolved contradictory documentation of showGeneralDialog and default value of 'barrierLabel' argument (#78890)

packages/flutter/lib/src/widgets/routes.dart

@@ -1870,11 +1870,11 @@ class RawDialogRoute<T> extends PopupRoute<T> {
 ///
 /// The `barrierDismissible` argument is used to determine whether this route
 /// can be dismissed by tapping the modal barrier. This argument defaults
-/// to true. If `barrierDismissible` is true, a non-null `barrierLabel` must be
+/// to false. If `barrierDismissible` is true, a non-null `barrierLabel` must be
 /// provided.
 ///
 /// The `barrierLabel` argument is the semantic label used for a dismissible
-/// barrier. This argument defaults to "Dismiss".
+/// barrier. This argument defaults to `null`.
 ///
 /// The `barrierColor` argument is the color used for the modal barrier. This
 /// argument defaults to `Color(0x80000000)`.

packages/flutter/test/widgets/routes_test.dart

@@ -1015,6 +1015,41 @@ void main() {
       expect(find.byType(ModalBarrier), findsNWidgets(1));
     });
 
+    testWidgets('showGeneralDialog uses null as a barrierLabel by default', (WidgetTester tester) async {
+      await tester.pumpWidget(MaterialApp(
+        home: Builder(
+          builder: (BuildContext context) {
+            return ElevatedButton(
+              onPressed: () {
+                showGeneralDialog<void>(
+                  context: context,
+                  transitionDuration: Duration.zero,
+                  pageBuilder: (BuildContext innerContext, _, __) {
+                    return const SizedBox();
+                  },
+                );
+              },
+              child: const Text('Show Dialog'),
+            );
+          },
+        ),
+      ));
+
+      // Open the dialog.
+      await tester.tap(find.byType(ElevatedButton));
+      await tester.pump();
+      expect(find.byType(ModalBarrier), findsNWidgets(2));
+      final ModalBarrier barrier = find.byType(ModalBarrier).evaluate().last.widget as ModalBarrier;
+      expect(barrier.semanticsLabel, same(null));
+
+      // Close the dialog.
+      final StatefulElement navigatorElement = find.byType(Navigator).evaluate().last as StatefulElement;
+      final NavigatorState navigatorState = navigatorElement.state as NavigatorState;
+      navigatorState.pop();
+      await tester.pumpAndSettle();
+      expect(find.byType(ModalBarrier), findsNWidgets(1));
+    });
+
     testWidgets('showGeneralDialog uses root navigator by default', (WidgetTester tester) async {
       final DialogObserver rootObserver = DialogObserver();
       final DialogObserver nestedObserver = DialogObserver();