Enable null_closures (#77095)

analysis_options.yaml

@@ -134,7 +134,7 @@ linter:
     # - no_runtimeType_toString # ok in tests; we enable this only in packages/
     - non_constant_identifier_names
     - null_check_on_nullable_type_parameter
-    # - null_closures # not required by flutter style
+    - null_closures
     # - omit_local_variable_types # opposite of always_specify_types
     # - one_member_abstracts # too many false positives
     # - only_throw_errors # https://github.com/flutter/flutter/issues/5792

dev/integration_tests/android_views/lib/motion_events_page.dart

@@ -227,7 +227,7 @@ class MotionEventsBodyState extends State<MotionEventsBody> {
         setState(() {});
         break;
     }
-    return Future<dynamic>.sync(null);
+    return Future<dynamic>.value(null);
   }
 
   Future<dynamic> onViewMethodChannelCall(MethodCall call) {
@@ -240,7 +240,7 @@ class MotionEventsBodyState extends State<MotionEventsBody> {
         setState(() {});
         break;
     }
-    return Future<dynamic>.sync(null);
+    return Future<dynamic>.value(null);
   }
 
   Widget buildEventTile(BuildContext context, int index) {

dev/integration_tests/hybrid_android_views/lib/motion_events_page.dart

@@ -199,7 +199,7 @@ class MotionEventsBodyState extends State<MotionEventsBody> {
         setState(() {});
         break;
     }
-    return Future<dynamic>.sync(null);
+    return Future<dynamic>.value(null);
   }
 
   Future<dynamic> onViewMethodChannelCall(MethodCall call) {
@@ -212,7 +212,7 @@ class MotionEventsBodyState extends State<MotionEventsBody> {
         setState(() {});
         break;
     }
-    return Future<dynamic>.sync(null);
+    return Future<dynamic>.value(null);
   }
 
   Widget buildEventTile(BuildContext context, int index) {