[rules-users] Null Pointer Exception in "org.drools.reteoo.RuleTerminalNode.retractTuple"

[Anstis, Michael (M.)]

Hi - me again :-(

Unfortunately I receive a NPE (3.1-M1) as follows (a complete JAR
illustrating the problem is available):-

**Java

Man man=new Man();
Machine machine=new Machine();
Process p = new Process();
wm.assertObject(man);
wm.assertObject(machine);
wm.assertObject(p);

**Rules

package drools.debug

rule "Rule-1"
no-loop true
when
	$p : Process()
then
	System.out.println("DEBUG [Rule-1]---> Add ProcessAlternative to
Process");
	ProcessAlternative pa = new ProcessAlternative();
	$p.addProcessAlternative(pa);
	assert(pa);
	modify($p);
end

rule "Rule-2"
no-loop true
when
	$m : Machine()
then
	System.out.println("DEBUG [Rule-2]---> Add Machine to
MachineEntry");
	MachineEntry me = new MachineEntry();
	me.setMachine($m);
	assert(me);
end

rule "Rule-3"
no-loop true
when
	$me : MachineEntry()
	$pa : ProcessAlternative()
then
	System.out.println("DEBUG [Rule-3]---> Add MachineEntry to
ProcessAlternative");
	$pa.addMachineEntry($me);
	modify($pa);
end

//rule "Rule-4 (Null Pointer Exception)"
//no-loop true
//when
//	$h : Man ( )
//	$m : Machine ( )
//	$mte : MachineEntry ( machine == $m )
//then
//	System.out.println("DEBUG [Rule 4]---> Assigned resource");
//	$m.setManualResource($h);
//	modify($m);
//end

**Output

DEBUG [Rule-1]---> Add ProcessAlternative to Process
DEBUG [Rule-2]---> Add Machine to MachineEntry
DEBUG [Rule-3]---> Add MachineEntry to ProcessAlternative

This is what I'd expect. If however rule "Rule-4" is uncommented the
output is:-

DEBUG [Rule-1]---> Add ProcessAlternative to Process
DEBUG [Rule-2]---> Add Machine to MachineEntry
DEBUG [Rule-3]---> Add MachineEntry to ProcessAlternative
DEBUG [Rule 4]---> Assigned resource
DEBUG [Rule-2]---> Add Machine to MachineEntry		<-- Why
activated? no-loop is true 
DEBUG [Rule 4]---> Assigned resource			<-- Presumably
activated as a consequence of above

And I receive a NPE with the following stack trace:-

java.lang.NullPointerException
	at
org.drools.reteoo.RuleTerminalNode.retractTuple(RuleTerminalNode.java:26
7)
	at
org.drools.reteoo.SingleTupleSinkAdapter.propagateRetractTuple(SingleTup
leSinkAdapter.java:38)
	at org.drools.reteoo.JoinNode.retractTuple(JoinNode.java:217)
	at
org.drools.reteoo.SingleTupleSinkAdapter.propagateRetractTuple(SingleTup
leSinkAdapter.java:38)
	at org.drools.reteoo.JoinNode.retractObject(JoinNode.java:183)
	at
org.drools.reteoo.CompositeObjectSinkAdapter.propagateRetractObject(Comp
ositeObjectSinkAdapter.java:369)
	at
org.drools.reteoo.ObjectTypeNode.retractObject(ObjectTypeNode.java:189)
	at org.drools.reteoo.Rete.retractObject(Rete.java:171)
	at
org.drools.reteoo.ReteooRuleBase.retractObject(ReteooRuleBase.java:215)
	at
org.drools.reteoo.ReteooWorkingMemory.doRetract(ReteooWorkingMemory.java
:76)
	at
org.drools.common.AbstractWorkingMemory.modifyObject(AbstractWorkingMemo
ry.java:940)
	at
org.drools.base.DefaultKnowledgeHelper.modifyObject(DefaultKnowledgeHelp
er.java:95)
	at
drools.debug.Rule_Rule_4__Null_Pointer_Exception__0.consequence(Rule_Rul
e_4__Null_Pointer_Exception__0.java:8)
	at
drools.debug.Rule_Rule_4__Null_Pointer_Exception__0ConsequenceInvoker.ev
aluate(Rule_Rule_4__Null_Pointer_Exception__0ConsequenceInvoker.java:24)
	at
org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:467)
	at
org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:431)
	at
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemo
ry.java:360)

I have also encountered NPE in
"org.drools.reteoo.AlphaNode.retractObject" when using my actual rules
other than these simplifications put together to demonstrate the error
(both are caused by a call to "final Activation activation =
tuple.getActivation();" returning NULL so I suspect the root cause to be
common). Is this a case for a new JIRA entry or have I done something
idiotic?

With kind regards,

Mike
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