Random Nullpointer

From time to time i.m getting weird Nullpointer exception. I didn't reproduce the problem when the app is deployed on Glassfish. Only on jetty and only on windows system (with MAC OS everything is ok)

Stacktrace:

java.lang.NullPointerException
at org.drools.base.evaluators.EvaluatorRegistry.addEvaluatorDefinition(EvaluatorRegistry.java:155)
at org.drools.base.evaluators.EvaluatorRegistry.<init>(EvaluatorRegistry.java:77)
at org.drools.compiler.PackageBuilderConfiguration.buildEvaluatorRegistry(PackageBuilderConfiguration.java:544)
at org.drools.compiler.PackageBuilderConfiguration.init(PackageBuilderConfiguration.java:196)
at org.drools.compiler.PackageBuilderConfiguration.<init>(PackageBuilderConfiguration.java:170)
at org.drools.compiler.PackageBuilder.<init>(PackageBuilder.java:308)
at org.drools.compiler.PackageBuilder.<init>(PackageBuilder.java:236)

And my code is a simple object creation:

PackageBuilder packageBuilder = new PackageBuilder();

Any hint why this might occur ? Or should i just ignore it because on production we have Glassfish server ?