fix: update _floatingActionButtonVisibility only if floatingActionButton is not null

Author: hello-coder-xu

packages/flutter/lib/src/material/scaffold.dart

@@ -3249,7 +3249,9 @@ class _StandardBottomSheetState extends State<_StandardBottomSheet> {
         _kMaxBottomSheetScrimOpacity - scaffold._floatingActionButtonVisibilityValue,
       ));
     } else {
-      scaffold._floatingActionButtonVisibilityValue = 1.0;
+      if (scaffold.widget.floatingActionButton != null) {
+        scaffold._floatingActionButtonVisibilityValue = 1.0;
+      }
       scaffold.showBodyScrim(false, 0.0);
     }
     // If the Scaffold.bottomSheet != null, we're a persistent bottom sheet.

packages/flutter/test/material/scaffold_test.dart

@@ -3395,6 +3395,83 @@ void main() {
     // FAB is not visible.
     expect(find.byType(FloatingActionButton), findsNothing);
   });
+
+  testWidgets('fix _floatingActionButtonVisibility update',
+      (WidgetTester tester) async {
+    final List<String> log = <String>[];
+
+    bool expanded = true;
+    final DraggableScrollableController controller =
+        DraggableScrollableController();
+    addTearDown(controller.dispose);
+    await tester.pumpWidget(
+      MaterialApp(
+        home: StatefulBuilder(
+          builder:
+              (BuildContext context, void Function(void Function()) setState) {
+            return Scaffold(
+              bottomSheet: expanded
+                  ? DraggableScrollableSheet(
+                      expand: false,
+                      snap: true,
+                      initialChildSize: 0.25,
+                      maxChildSize: 0.5,
+                      snapSizes: const <double>[0.5],
+                      controller: controller,
+                      builder: (BuildContext context,
+                          ScrollController scrollController) {
+                        return SingleChildScrollView(
+                          controller: scrollController,
+                          child: Column(
+                            children: <Widget>[
+                              TextButton(
+                                onPressed: () {
+                                  controller.animateTo(
+                                    0.5,
+                                    duration: Durations.short4,
+                                    curve: Curves.easeIn,
+                                  );
+                                },
+                                child: const Text('Toggle'),
+                              )
+                            ],
+                          ),
+                        );
+                      },
+                    )
+                  : null,
+              floatingActionButton: expanded
+                  ? FloatingActionButton(
+                      onPressed: () {
+                        setState(() {
+                          expanded = !expanded;
+                        });
+                      },
+                      child: const Icon(Icons.add),
+                    )
+                  : null,
+            );
+          },
+        ),
+      ),
+    );
+
+    await tester.tap(find.byType(TextButton));
+    await tester.pumpAndSettle();
+
+    final double controllerValue = controller.size;
+    expect(controllerValue, 0.5);
+
+    await tester.tap(find.byType(FloatingActionButton));
+
+    final FlutterExceptionHandler? handler = FlutterError.onError;
+    FlutterError.onError = (FlutterErrorDetails details) {
+      log.add(details.exception.toString());
+    };
+    await tester.pump();
+    FlutterError.onError = handler;
+    expect(log.length, 0);
+  });
 }
 
 class _GeometryListener extends StatefulWidget {