Issue 3931. Visit children nodes safely.

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

Index: compiler/java/com/google/dart/compiler/ast/DartDoWhileStatement.java
diff --git a/compiler/java/com/google/dart/compiler/ast/DartDoWhileStatement.java b/compiler/java/com/google/dart/compiler/ast/DartDoWhileStatement.java
index 03353e09752ddb068969f85247dedb52da9884eb..a2a42695934c03ea8fba58002898c5919e004f82 100644
--- a/compiler/java/com/google/dart/compiler/ast/DartDoWhileStatement.java
+++ b/compiler/java/com/google/dart/compiler/ast/DartDoWhileStatement.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.
 
@@ -27,10 +27,8 @@ public class DartDoWhileStatement extends DartStatement {
 
   @Override
   public void visitChildren(ASTVisitor<?> visitor) {
-    if (condition != null) {
-      condition.accept(visitor);
-    }
-    body.accept(visitor);
+    safelyVisitChild(condition, visitor);
+    safelyVisitChild(body, visitor);
   }
 
   @Override