Issue 3931. Visit children nodes safely.

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

Index: compiler/java/com/google/dart/compiler/ast/DartFunction.java
diff --git a/compiler/java/com/google/dart/compiler/ast/DartFunction.java b/compiler/java/com/google/dart/compiler/ast/DartFunction.java
index 2c28f807e96729f093e934c2eef291ad589ac591..e51be2a70de7669f6be9afd26513be78c64d5410 100644
--- a/compiler/java/com/google/dart/compiler/ast/DartFunction.java
+++ b/compiler/java/com/google/dart/compiler/ast/DartFunction.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.
 
@@ -36,12 +36,8 @@ public class DartFunction extends DartNode {
   @Override
   public void visitChildren(ASTVisitor<?> visitor) {
     parameters.accept(visitor);
-    if (body != null) {
-      body.accept(visitor);
-    }
-    if (returnTypeNode != null) {
-      returnTypeNode.accept(visitor);
-    }
+    safelyVisitChild(body, visitor);
+    safelyVisitChild(returnTypeNode, visitor);
   }
 
   @Override