[rules-users] is null or is not Null failing for a String field check in Guvnor drl

Hi , when using a business rule guided editor , for a fact, when I select a string type field from the drl guided editor in Guvnor  and select  is null from the dropdown list of operators, I get the following validation error when I do a validate on the rule. no viable alternative at input 'null' in rule "Asset_Description_NullCheckRule" when I do a View Source, it shows the source as when             Asset( description == null null ) Is this a bug ? if I select the free form drl option and create the when condition as Asset( description == null ) , it validates fine. Thanks, Ram