ClassCastException in RuleTerminalNode.retractLeftTuple()

import org.drools.Person;
import org.drools.Cheese;
rule R1
ruleflow-group "group1"
lock-on-active true
when
   $p : Person()
then
   $p.setName("John");
   update ($p);
end
rule R2
ruleflow-group "group1"
lock-on-active true
when
   $p : Person( name == null )
   forall ( Cheese ( type == "cheddar" ))
then
end

Exception executing consequence for rule "R1" in defaultpkg: java.lang.ClassCastException: java.lang.Boolean cannot be cast to org.drools.spi.Activation
	at org.drools.runtime.rule.impl.DefaultConsequenceExceptionHandler.handleException(DefaultConsequenceExceptionHandler.java:39)
	at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:1287)
	at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:1212)
	at org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1446)
	at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:710)
	at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:674)
	at org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:230)
...
Caused by: java.lang.ClassCastException: java.lang.Boolean cannot be cast to org.drools.spi.Activation
	at org.drools.reteoo.RuleTerminalNode.retractLeftTuple(RuleTerminalNode.java:309)
	at org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateRetractLeftTuple(SingleLeftTupleSinkAdapter.java:224)
	at org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateRetractLeftTuple(SingleLeftTupleSinkAdapter.java:98)
	at org.drools.reteoo.NotNode.retractLeftTuple(NotNode.java:216)
	at org.drools.reteoo.LeftTupleSource.doModifyLeftTuple(LeftTupleSource.java:286)
	at org.drools.reteoo.AbstractTerminalNode.modifyLeftTuple(AbstractTerminalNode.java:104)
	at org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateModifyLeftTuple(SingleLeftTupleSinkAdapter.java:205)
	at org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateModifyObject(SingleLeftTupleSinkAdapter.java:235)
	at org.drools.reteoo.LeftInputAdapterNode.modifyObject(LeftInputAdapterNode.java:170)
	at org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateModifyObject(CompositeObjectSinkAdapter.java:507)
	at org.drools.reteoo.CompositeObjectSinkAdapter.propagateModifyObject(CompositeObjectSinkAdapter.java:432)
	at org.drools.reteoo.ObjectTypeNode.modifyObject(ObjectTypeNode.java:314)
	at org.drools.reteoo.EntryPointNode.modifyObject(EntryPointNode.java:265)
	at org.drools.common.NamedEntryPoint.update(NamedEntryPoint.java:470)
	at org.drools.common.NamedEntryPoint.update(NamedEntryPoint.java:370)
	at org.drools.base.DefaultKnowledgeHelper.update(DefaultKnowledgeHelper.java:319)
	at defaultpkg.Rule_R1_71208af44b274026888141d4be342303.defaultConsequence(Rule_R1_71208af44b274026888141d4be342303.java:8)
	at defaultpkg.Rule_R1_71208af44b274026888141d4be342303DefaultConsequenceInvokerGenerated.evaluate(Unknown Source)
	at defaultpkg.Rule_R1_71208af44b274026888141d4be342303DefaultConsequenceInvoker.evaluate(Unknown Source)
	at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:1277)
	... 35 more

    public boolean createActivation(final LeftTuple tuple,
                                    final PropagationContext context,
                                    final InternalWorkingMemory workingMemory,
                                    final RuleTerminalNode rtn,
                                    final boolean reuseActivation ) {

...
            InternalAgendaGroup agendaGroup = (InternalAgendaGroup) getAgendaGroup( rule.getAgendaGroup() );
            if ( rule.getRuleFlowGroup() == null ) {
                // No RuleFlowNode so add it directly to the Agenda
                // do not add the activation if the rule is "lock-on-active" and the
                // AgendaGroup is active
                if ( rule.isLockOnActive() && agendaGroup.isActive() && agendaGroup.getAutoFocusActivator() != context) {
                        if ( tuple.getObject() == null ) {
                                tuple.setObject( Boolean.TRUE ); // this is so we can do a check with a bit more intent than a null check on modify
                        }
                    return false;
                }
            } else {
                // There is a RuleFlowNode so add it there, instead of the Agenda
                InternalRuleFlowGroup rfg = (InternalRuleFlowGroup) getRuleFlowGroup( rule.getRuleFlowGroup() );

                // do not add the activation if the rule is "lock-on-active" and the
                // RuleFlowGroup is active
                if ( rule.isLockOnActive() && rfg.isActive() && agendaGroup.getAutoFocusActivator() != context) {
                        if ( tuple.getObject() == null ) {
                                tuple.setObject( Boolean.TRUE ); // this is so we can do a check with a bit more intent than a null check on modify
                        }
                    return false;
                }
            }