I'm trying out stream mode and having some trouble. I'm setting drools.eventProcessingMode to stream and using an entry point for inserting some objects. Sometimes (but not all of the time) the rule that matches on objects from the entry point (currently the only rule in the ruleset) will get a null reference for the object retrieved from the entry point. Here's the drl: declare Incoming @role( event ) @expires( 15s ) end rule "entry" no-loop true when i: Incoming() from entry-point "Incoming"; e: Existing(matcher == i.matcher); then if(i == null) { System.err.println("NULL MATCHED WITH " + e.getMatcher()); } else { if(e.incorporate(i)) { update(e); System.out.println(e); } } end Sometimes (not not all of the time) I get these in stderr: NULL MATCHED WITH Matcher1 NULL MATCHED WITH Matcher12 NULL MATCHED WITH Matcher3 NULL MATCHED WITH Matcher9 The Incoming objects are added at a high rate (sometimes thousands per second) so my guess was that they weren't being processed fast enough and were being expired before the rule action could fire. I changed their @expires value to "1d" and then got one of the two exceptions below when I ran the application. Some more details: I use WorkingMemoryEntryPoint.insert() to add the Incoming objects. The StatefulKnowledgeSession runs in a separate thread, blocking on fireUntilHalt(). Here are the exceptions I often incur on calling WorkingMemoryEntryPoint.insert() with the long expiration. Rule execution halts after the exception: Exception in thread "Thread-5" java.lang.NullPointerException at org.drools.util.RightTupleList.matches(RightTupleList.java:167) at org.drools.util.RightTupleIndexHashTable.get(RightTupleIndexHashTable.java:292) at org.drools.util.RightTupleIndexHashTable.getFirst(RightTupleIndexHashTable.java:87) at org.drools.reteoo.JoinNode.assertLeftTuple(JoinNode.java:112) at org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:117) at org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:28) at org.drools.reteoo.JoinNode.assertObject(JoinNode.java:175) at org.drools.reteoo.SingleObjectSinkAdapter.propagateAssertObject(SingleObjectSinkAdapter.java:42) at org.drools.reteoo.PropagationQueuingNode$AssertAction.execute(PropagationQueuingNode.java:326) at org.drools.reteoo.PropagationQueuingNode.propagateActions(PropagationQueuingNode.java:221) at org.drools.reteoo.PropagationQueuingNode$PropagateAction.execute(PropagationQueuingNode.java:394) at org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:1464) at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:156) at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:120) at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:78) at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:26) at org.gregcode.stuff.analysis.Analyzer.add(Analyzer.java:108) at org.gregcode.stuff.Simulator$1.run(Simulator.java:69) at java.lang.Thread.run(Thread.java:619) Exception in thread "Thread-3" java.lang.NullPointerException at org.drools.util.LeftTupleList.add(LeftTupleList.java:48) at org.drools.reteoo.RuleTerminalNode.assertLeftTuple(RuleTerminalNode.java:245) at org.drools.reteoo.RuleTerminalNode.assertLeftTuple(RuleTerminalNode.java:165) at org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:117) at org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:28) at org.drools.reteoo.JoinNode.assertLeftTuple(JoinNode.java:116) at org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:117) at org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:28) at org.drools.reteoo.JoinNode.assertObject(JoinNode.java:175) at org.drools.reteoo.SingleObjectSinkAdapter.propagateAssertObject(SingleObjectSinkAdapter.java:42) at org.drools.reteoo.PropagationQueuingNode$AssertAction.execute(PropagationQueuingNode.java:326) at org.drools.reteoo.PropagationQueuingNode.propagateActions(PropagationQueuingNode.java:221) at org.drools.reteoo.PropagationQueuingNode$PropagateAction.execute(PropagationQueuingNode.java:394) at org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:1464) at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:156) at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:120) at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:78) at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:26) at org.gregcode.stuff.analysis.Analyzer.add(Analyzer.java:108) at org.gregcode.stuff.Simulator$1.run(Simulator.java:69) at java.lang.Thread.run(Thread.java:619) Thanks! GreG