[rules-users] Throws NPE when comparing one property to another of the same bean class

[Miles Wen]

That's almost all the details in the mail subject; When I am running this
rule in drools 5.1.0:

package com.sample

import com.sample.Msg;
import java.util.Date;

rule "Hello World"
    when
        m1:Msg()
        m:Msg(dbl > lo || m1.in == in)
    then
end

The java bean named 'Msg' definition:

package com.sample;

import java.util.Date;
import java.util.HashSet;
import java.util.Set;

public class Msg {
    private Long lo = 5l;
    private double dbl = 5.5;
    private Date date = new Date();
    private int in = 4;
    private boolean bool;
    private Set<String> set = new HashSet<String>();
... // getter and setters ignored

then it throws exception :

java.lang.NullPointerException
    at org.drools.reteoo.LeftTuple.get(LeftTuple.java:399)
    at org.drools.reteoo.LeftTuple.get(LeftTuple.java:434)
    at
org.drools.rule.VariableRestriction$DoubleVariableContextEntry.updateFromTuple(VariableRestriction.java:563)
    at
org.drools.rule.AbstractCompositeConstraint$MultiFieldConstraintContextEntry.updateFromTuple(AbstractCompositeConstraint.java:306)
    at
org.drools.common.SingleBetaConstraints.updateFromTuple(SingleBetaConstraints.java:123)
    at org.drools.reteoo.JoinNode.assertLeftTuple(JoinNode.java:77)
    at
org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:189)
    at
org.drools.reteoo.SingleLeftTupleSinkAdapter.createAndPropagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:138)
    at
org.drools.reteoo.LeftInputAdapterNode.assertObject(LeftInputAdapterNode.java:148)
    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 com.sample.DroolsTest.main(DroolsTest.java:43)

I think I am doing nothing wrong with the code, is this a bug or something?
Or just comparing properties in the same bean class is illegal?
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