CTP to RTM upgrade - How to use formatter

Hi,

In CTP version, I used to write below code to save the changes to file with the formatting. Any idea what is changed in RTM?

 IEnumerable<IFormattingRule> rules =  FormattingRules.GetDefaultRules("C#");
                File.WriteAllText(
                    filePath,
                    modifiedTree.Format(FormattingOptions.GetDefaultOptions(), rules).GetFormattedRoot().ToFullString());