[rules-users] NullPointerException at org.mvel2.ast.IntSub.getReducedValueAccelerated

Hi, When starting the planning solver I sometimes get the error as listed beneath. I think it happens about 1 out of 5 runs. It doesn't seem to have much influence on the solving process as everything continues normally (I think). I do not use any mvel expressions to my knowledge. Anyway, it would be nice to understand why this happens and how to get this resolved. Exception in thread "Thread-1" java.lang.NullPointerException     at org.mvel2.ast.IntSub.getReducedValueAccelerated(IntSub.java:17)     at org.mvel2.compiler.ExecutableAccessor.getValue(ExecutableAccessor.java:38)     at org.mvel2.ast.Substatement.getReducedValueAccelerated(Substatement.java:44)     at org.mvel2.ast.BinaryOperation.getReducedValueAccelerated(BinaryOperation.java:108)     at org.mvel2.ast.And.getReducedValueAccelerated(And.java:34)     at org.mvel2.MVELRuntime.execute(MVELRuntime.java:85)     at org.mvel2.compiler.CompiledExpression.getDirectValue(CompiledExpression.java:123)     at org.mvel2.compiler.CompiledExpression.getValue(CompiledExpression.java:119)     at org.mvel2.compiler.CompiledExpression.getValue(CompiledExpression.java:113)     at org.mvel2.MVEL.executeExpression(MVEL.java:930)     at org.drools.rule.constraint.MvelConditionEvaluator.evaluate(MvelConditionEvaluator.java:70)     at org.drools.rule.constraint.MvelConditionEvaluator.ensureBranchEvaluation(MvelConditionEvaluator.java:117)     at org.drools.rule.constraint.MvelConditionEvaluator.ensureCompleteEvaluation(MvelConditionEvaluator.java:102)     at org.drools.rule.constraint.MvelConditionEvaluator.ensureCompleteEvaluation(MvelConditionEvaluator.java:90)     at org.drools.rule.constraint.MvelConditionEvaluator.getAnalyzedCondition(MvelConditionEvaluator.java:82)     at org.drools.rule.constraint.MvelConstraint.executeJitting(MvelConstraint.java:270)     at org.drools.rule.constraint.MvelConstraint.access$200(MvelConstraint.java:51)     at org.drools.rule.constraint.MvelConstraint$ConditionJitter.run(MvelConstraint.java:250)     at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)     at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)     at java.lang.Thread.run(Unknown Source)   Thanks, Michiel ----------------- http://www.codessentials.com - Your essential software, for free! Follow us at http://twitter.com/#!/Codessentials