[rules-users] NullPointerException in a simple test -- a Drools bug?

Hi all, I'm trying to migrate my JBoss v3.0.6 rules to the latest v4.0.0 release. I could already resolve some issues but now I'm already stuck for hours with a NullPointerException that I can't get rid of. I broke the problem down to a relatively small set of test files that I'd like to show you here: /* SimpleTest.java */ package com.sample; // ... imports removed for brevity public class SimpleTest { public static final void main(String[] args) throws Exception { PackageBuilder builder = new PackageBuilder(); builder.addPackageFromDrl(new InputStreamReader(SimpleTest.class .getResourceAsStream("/rf1.drl"))); builder.addPackageFromDrl(new InputStreamReader(SimpleTest.class .getResourceAsStream("/rf2.drl"))); RuleBase rb = RuleBaseFactory.newRuleBase(); rb.addPackage(builder.getPackage()); WorkingMemory wm = rb.newStatefulSession(); wm.insert(new Task()); // <-- crashes here wm.fireAllRules(); } } /* Task.java */ package com.sample; public class Task { private String next = null; public String getNext() { return next; } public void setNext(String next) { this.next = next; } } // rf1.drl package com.sample rule "r0" when Task( next == null ); # <-- change to "x" then System.out.println("r0"); end rule "r1" when Task( next == "1" ); then System.out.println("r1"); end // rf2.drl package com.sample rule "r2" when Task( next == "2" ); then System.out.println("r1"); end As you can see there are two Drools rule files and two Java classes. If I run the SimpleTest class, I get the following exception: Exception in thread "main" java.lang.NullPointerException at org.drools.reteoo.CompositeObjectSinkAdapter$HashKey.equals(CompositeObjectSinkAdapter.java:608) at org.drools.util.AbstractHashTable$EqualityEquals.equal(AbstractHashTable.java:345) at org.drools.util.ObjectHashMap.get(ObjectHashMap.java:86) at org.drools.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:295) at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:168) at org.drools.reteoo.Rete.assertObject(Rete.java:168) at org.drools.reteoo.ReteooRuleBase.assertObject(ReteooRuleBase.java:190) at org.drools.reteoo.ReteooWorkingMemory.doInsert(ReteooWorkingMemory.java:70) at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:848) at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:822) at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:623) at com.sample.SimpleTest.main(SimpleTest.java:22) I've marked the position in the source code at which the run crashes. Does anybody have an idea what's wrong here? Some more strange things relating to this problem: * If I change the 'null' in rf1.drl to '""' (empty string), the problem remains. * If I change the 'null' in rf1.drl to '"x"' (or some other non-empty string), then the exception is gone. * If I remove any of the two rule files, the exception is gone, too. Any ideas? Should I file a bug? Thanks in advance! Cheers, Christian