enable prefer_null_aware_operators (#77105)

analysis_options.yaml

@@ -175,7 +175,7 @@ linter:
     - prefer_is_not_operator
     - prefer_iterable_whereType
     # - prefer_mixin # https://github.com/dart-lang/language/issues/32
-    # - prefer_null_aware_operators # disable until NNBD, see https://github.com/flutter/flutter/pull/32711#issuecomment-492930932
+    - prefer_null_aware_operators
     # - prefer_relative_imports # not yet tested
     - prefer_single_quotes
     - prefer_spread_collections

packages/flutter/lib/src/gestures/arena.dart

@@ -267,7 +267,7 @@ class GestureArenaManager {
   bool _debugLogDiagnostic(int pointer, String message, [ _GestureArena? state ]) {
     assert(() {
       if (debugPrintGestureArenaDiagnostics) {
-        final int? count = state != null ? state.members.length : null;
+        final int? count = state?.members.length;
         final String s = count != 1 ? 's' : '';
         debugPrint('Gesture arena ${pointer.toString().padRight(4)} ❙ $message${ count != null ? " with $count member$s." : ""}');
       }

packages/flutter/test/material/dropdown_form_field_test.dart

@@ -65,7 +65,7 @@ Widget buildFormFrame({
             iconEnabledColor: iconEnabledColor,
             isDense: isDense,
             isExpanded: isExpanded,
-            items: items == null ? null : items.map<DropdownMenuItem<String>>((String item) {
+            items: items?.map<DropdownMenuItem<String>>((String item) {
               return DropdownMenuItem<String>(
                 key: ValueKey<String>(item),
                 value: item,

packages/flutter/test/material/dropdown_test.dart

@@ -54,9 +54,7 @@ Widget buildDropdown({
     Color? focusColor,
     Color? dropdownColor,
   }) {
-  final List<DropdownMenuItem<String>>? listItems = items == null
-      ? null
-      : items.map<DropdownMenuItem<String>>((String item) {
+  final List<DropdownMenuItem<String>>? listItems = items?.map<DropdownMenuItem<String>>((String item) {
     return DropdownMenuItem<String>(
       key: ValueKey<String>(item),
       value: item,

packages/flutter_tools/lib/src/ios/simulators.dart

@@ -692,7 +692,7 @@ class _IOSSimulatorLogReader extends DeviceLogReader {
       onListen: _start,
       onCancel: _stop,
     );
-    _appName = app == null ? null : app.name.replaceAll('.app', '');
+    _appName = app?.name?.replaceAll('.app', '');
   }
 
   final IOSSimulator device;