Fix ConvertToSwitchExpression when SwitchStatement is empty.

Change-Id: Id7ab8319ff5a9e41b353ed1363ce0d5159fe4ff2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/292984
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

pkg/analysis_server/lib/src/services/correction/dart/convert_to_switch_expression.dart

@@ -13,6 +13,7 @@ import 'package:analyzer_plugin/utilities/assist/assist.dart';
 import 'package:analyzer_plugin/utilities/change_builder/change_builder_core.dart';
 import 'package:analyzer_plugin/utilities/change_builder/change_builder_dart.dart';
 import 'package:analyzer_plugin/utilities/range_factory.dart';
+import 'package:collection/collection.dart';
 
 class ConvertToSwitchExpression extends CorrectionProducer {
   /// Local variable reference used in assignment switch expression generation.
@@ -309,7 +310,7 @@ class ConvertToSwitchExpression extends CorrectionProducer {
   bool isEffectivelyExhaustive(DartType? type, SwitchStatement node) {
     if (type == null) return false;
     if ((typeSystem as TypeSystemImpl).isAlwaysExhaustive(type)) return true;
-    var last = node.members.last;
+    var last = node.members.lastOrNull;
     if (last is SwitchPatternCase) {
       var pattern = last.guardedPattern.pattern;
       return pattern is WildcardPattern;

pkg/analysis_server/test/src/services/correction/assist/convert_to_switch_expression_test.dart

@@ -297,6 +297,15 @@ String f(String s) {
 ''');
   }
 
+  Future<void> test_empty() async {
+    await resolveTestCode('''
+void f(int x) {
+  switch (x) {}
+}
+''');
+    await assertNoAssistAt('(x)');
+  }
+
   Future<void> test_return_notExhaustive_noAssist() async {
     await resolveTestCode('''
 String f(int i) {