Issue 3931. Visit children nodes safely.

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

-// 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.
 
 package com.google.dart.compiler.ast;
 
 import java.util.List;
 
 /**
  * Represents a Dart function.
  */
@@ skipping 17 matching lines @@
     return parameters;
   }
 
   public DartTypeNode getReturnTypeNode() {
     return returnTypeNode;
   }
 
   @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
   public <R> R accept(ASTVisitor<R> visitor) {
     return visitor.visitFunction(this);
   }
 }