ExitDetector: Do not special case enums, since null exists

pkg/analyzer/test/generated/all_the_rest_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.test.generated.all_the_rest_test;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
@@ skipping 3898 matching lines @@
 enum E { A, B }
 String f(E e) {
   switch (e) {
     case A:
       return 'A';
     case B:
       return 'B';
   }
 }
 ''');
-    _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) {
   switch (e) {
     case A:
       return 'A';
     default:
       return '?';
   }
 }
 ''');
     _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() {
   x: while (true) {
     if (1 < 2) {
       break x;
     }
     return;
   }
 }
@@ skipping 444 matching lines @@
     expect(UriKind.fromEncoding(0x70), same(UriKind.PACKAGE_URI));
     expect(UriKind.fromEncoding(0x58), same(null));
   }
 
   void test_getEncoding() {
     expect(UriKind.DART_URI.encoding, 0x64);
     expect(UriKind.FILE_URI.encoding, 0x66);
     expect(UriKind.PACKAGE_URI.encoding, 0x70);
   }
 }