corrected faulty getValueAsCode() method in SaveFolderStringType

Sorry, had to correct one error in the getValueAsCode() method.
Could you please make sure that this implementation is really correct, since I am not overly enthusiastic as to whether or not I have understood what exactly this method is supposed to do?
However, with this implementation, no errors are thrown on saving a project containing an object of this type (in contrast to the previous implementation).