Issue 3931. Visit children nodes safely.

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

Index: compiler/java/com/google/dart/compiler/ast/DartLabel.java
diff --git a/compiler/java/com/google/dart/compiler/ast/DartLabel.java b/compiler/java/com/google/dart/compiler/ast/DartLabel.java
index c9405fd610b2ec2c329da5ce836108c18d211107..1efdbe384d4d3e861e747f5ddbf3f594ded3b2e0 100644
--- a/compiler/java/com/google/dart/compiler/ast/DartLabel.java
+++ b/compiler/java/com/google/dart/compiler/ast/DartLabel.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.
 
@@ -53,10 +53,8 @@ public class DartLabel extends DartStatement {
 
   @Override
   public void visitChildren(ASTVisitor<?> visitor) {
-    label.accept(visitor);
-    if (statement != null) {
-      statement.accept(visitor);
-    }
+    safelyVisitChild(label, visitor);
+    safelyVisitChild(statement, visitor);
   }
 
   @Override