Issue 3931. Visit children nodes safely.

compiler/java/com/google/dart/compiler/ast/DartSwitchStatement.java

Index: compiler/java/com/google/dart/compiler/ast/DartSwitchStatement.java
diff --git a/compiler/java/com/google/dart/compiler/ast/DartSwitchStatement.java b/compiler/java/com/google/dart/compiler/ast/DartSwitchStatement.java
index 816827d0ef907c24c515a47bf3bdddf640bcb9ff..985ec00d4748d7b73b7eafbcd345e2e5a2acf2b1 100644
--- a/compiler/java/com/google/dart/compiler/ast/DartSwitchStatement.java
+++ b/compiler/java/com/google/dart/compiler/ast/DartSwitchStatement.java
@@ -1,4 +1,4 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2012, 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.
 
@@ -29,7 +29,7 @@ public class DartSwitchStatement extends DartStatement {
 
   @Override
   public void visitChildren(ASTVisitor<?> visitor) {
-    expression.accept(visitor);
+    safelyVisitChild(expression, visitor);
     members.accept(visitor);
   }