NullPointerException in addPackage in Drools

Caused by: java.lang.NullPointerException
at org.drools.reteoo.CompositeObjectSinkAdapter.unregisterFieldIndex(CompositeObjectSinkAdapter.java:313)
at org.drools.reteoo.CompositeObjectSinkAdapter.removeObjectSink(CompositeObjectSinkAdapter.java:163)
at org.drools.reteoo.ObjectSource.removeObjectSink(ObjectSource.java:167)
at org.drools.reteoo.ObjectTypeNode.doRemove(ObjectTypeNode.java:355)
at org.drools.reteoo.ObjectTypeNode.remove(ObjectTypeNode.java:325)
at org.drools.reteoo.ObjectSource.doRemove(ObjectSource.java:209)
at org.drools.common.BaseNode.remove(BaseNode.java:109)
at org.drools.reteoo.ObjectSource.doRemove(ObjectSource.java:209)
at org.drools.common.BaseNode.remove(BaseNode.java:109)
at org.drools.reteoo.BetaNode.doRemove(BetaNode.java:289)
at org.drools.common.BaseNode.remove(BaseNode.java:109)
at org.drools.reteoo.BetaNode.doRemove(BetaNode.java:293)
at org.drools.common.BaseNode.remove(BaseNode.java:109)
at org.drools.reteoo.QueryTerminalNode.doRemove(QueryTerminalNode.java:252)
at org.drools.common.BaseNode.remove(BaseNode.java:109)
at org.drools.reteoo.ReteooBuilder.removeRule(ReteooBuilder.java:237)
at org.drools.reteoo.ReteooRuleBase.removeRule(ReteooRuleBase.java:432)
at org.drools.common.AbstractRuleBase.removeRule(AbstractRuleBase.java:831)
at org.drools.common.AbstractRuleBase.mergePackage(AbstractRuleBase.java:623)
at org.drools.common.AbstractRuleBase.addPackages(AbstractRuleBase.java:539)
at org.drools.reteoo.ReteooRuleBase.addPackages(ReteooRuleBase.java:445)
at org.drools.reteoo.ReteooRuleBase.addPackage(ReteooRuleBase.java:452)
at n3_project.helpers.N3SourcetoDrools.droolsCompile(N3SourcetoDrools.java:389)