ExitDetector: Do not special case enums, since null exists

pkg/analyzer/test/generated/all_the_rest_test.dart

Index: pkg/analyzer/test/generated/all_the_rest_test.dart
diff --git a/pkg/analyzer/test/generated/all_the_rest_test.dart b/pkg/analyzer/test/generated/all_the_rest_test.dart
index 3594bfbb5972891ffcaefa716b592d85b633a6fc..fcf09dee47dbea8966b6d5a44f4c9f13fd799970 100644
--- a/pkg/analyzer/test/generated/all_the_rest_test.dart
+++ b/pkg/analyzer/test/generated/all_the_rest_test.dart
@@ -3916,10 +3916,10 @@ String f(E e) {
   }
 }
 ''');
-    _assertNthStatementExits(source, 0);
+    _assertNthStatementDoesNotExit(source, 0);
   }
 
-  void test_switch_withEnum_true_withDefault() {
+  void test_switch_withEnum_true_withExitingDefault() {
     Source source = addSource(r'''
 enum E { A, B }
 String f(E e) {
@@ -3934,6 +3934,22 @@ String f(E e) {
     _assertNthStatementExits(source, 0);
   }
 
+  void test_switch_withEnum_true_withNonExitingDefault() {
+    Source source = addSource(r'''
+enum E { A, B }
+String f(E e) {
+  var x;
+  switch (e) {
+    case A:
+      return 'A';
+    default:
+      x = '?';
+  }
+}
+''');
+    _assertNthStatementDoesNotExit(source, 1);
+  }
+
   void test_whileStatement_breakWithLabel() {
     Source source = addSource(r'''
 void f() {