[rules-users] "not contains" on Java5 enumeration

I'm not certain, but it looks like the Operator "not contains"[1] works fine with strings but not Enumerations. Would someone please confirm or correct the rule syntax? Thank you. Given: rule "Absence_Accumulation_Rule" when $slice : TimeSlice( classifiers contains(TimeSliceClassifiers.ABSENCE), classifiers contains(TimeSliceClassifiers.OT), classifiers not contains (TimeSliceClassifiers.COUNT_TO_FLSA), then System.out.println("Absence: Count to overtime but not FLSA"); end public enum TimeSliceClassifiers { INSIDE_SCHEDULE, OUTSIDE_SCHEDULE, WORKED, ABSENCE, APPROVED, OVERTIME_REQUEST, CASH,INVOLUNTARY, COUNT_TO_OT, COUNT_TO_FLSA, OT, STRAIGHT, PREMIUM, EC0100, EC1400, EC1405 } public class TimeSlice { private Date start; private Date end; private int elapsed; private Set<TimeSliceClassifiers> classifiers; private boolean sliceCreatedByRules = false; } Provides the following error: [ERR 103] Line 110:21 rule 'in_key' failed predicate: {(validateIdentifierKey(DroolsSoftKeywords.IN))}? in rule "Absence_Accumulation_Rule" in pattern TimeSlice