CCE when using undeclared events

It may not be possible to avoid a runtime error because the parser does not "understand" temporal operators although it should not be impossible to add this. But is should be possible to produce an error message that clearly indicates the problem, e.g., "Cannot use operator xxx on fact type YYY which is not an event" or "YYY must be declared with @role(event) when using temporal operators".

Omitting the declares for events, as in this DRL:

/**
declare CallStart
@role( event )
@timestamp( time )
end

declare CallEnd
@role( event )
@timestamp( time )
end
**/

rule "match-start-end"
when
$start: CallStart( $s: source, $d: destination, $st: time )
not CallStart( this before $start )
$end: CallEnd( source == $s, destination == $d, $et: time )
not CallEnd( source == $s, destination == $d, this before $end )
then
//...
end

results in a runtime exception:

Exception in thread "main" java.lang.ClassCastException: org.drools.common.DefaultFactHandle cannot be cast to org.drools.common.EventFactHandle
at org.drools.base.evaluators.BeforeEvaluatorDefinition$BeforeEvaluator.evaluateCachedRight(BeforeEvaluatorDefinition.java:316)
at org.drools.rule.VariableRestriction.isAllowedCachedRight(VariableRestriction.java:117)
at org.drools.rule.VariableConstraint.isAllowedCachedRight(VariableConstraint.java:121)
at org.drools.common.SingleBetaConstraints.isAllowedCachedRight(SingleBetaConstraints.java:151)
at org.drools.reteoo.NotNode.assertObject(NotNode.java:140)
at org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:450)
at org.drools.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:378)
at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:190)
at org.drools.reteoo.EntryPointNode.assertObject(EntryPointNode.java:145)
at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:1174)
at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:1123)
at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:917)
at org.drools.impl.StatefulKnowledgeSessionImpl.insert(StatefulKnowledgeSessionImpl.java:251)
at call.Main.execute(Main.java:90)
at call.Main.main(Main.java:100)