I'm trying out the traits feature and I'm having some problems. I'm preparing simple Monkeys and Bananas example with existing classes that I want to add traits, but when I try adding a trait (either declared in DRL or as a static interface) I'm getting an exception thrown from the call to don(). Here's the code: declare HungryMonkey @format(trait) end rule "foo" when monkey : Monkey( ) then HungryMonkey hm = don(monkey, HungryMonkey.class); end And the exception thrown: Exception in thread "main" Exception executing consequence for rule "foo" in org.gregcode.mnb: org.drools.RuntimeDroolsException: Field/method 'attachment' not found for class 'org.gregcode.mnb.MonkeyWrapper' at org.drools.runtime.rule.impl.DefaultConsequenceExceptionHandler.handleException(DefaultConsequenceExceptionHandler.java:39) at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:1101) at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:1029) at org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1251) at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:709) at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:673) at org.gregcode.mnb.Main.main(Main.java:49) Caused by: org.drools.RuntimeDroolsException: Field/method 'attachment' not found for class 'org.gregcode.mnb.MonkeyWrapper' at org.drools.base.ClassFieldAccessorFactory.getClassFieldWriter(ClassFieldAccessorFactory.java:199) at org.drools.base.ClassFieldAccessorCache$CacheEntry.getWriteAccessor(ClassFieldAccessorCache.java:187) at org.drools.base.ClassFieldAccessorCache.getWriteAcessor(ClassFieldAccessorCache.java:116) at org.drools.base.ClassFieldAccessorStore.wire(ClassFieldAccessorStore.java:424) at org.drools.base.ClassFieldAccessorStore.getAccessor(ClassFieldAccessorStore.java:216) at org.drools.factmodel.traits.TraitFactory.buildWrapperClassDefinition(TraitFactory.java:340) at org.drools.factmodel.traits.TraitFactory.getCoreWrapper(TraitFactory.java:310) at org.drools.base.DefaultKnowledgeHelper.don(DefaultKnowledgeHelper.java:493) at org.drools.base.DefaultKnowledgeHelper.don(DefaultKnowledgeHelper.java:522) at org.gregcode.mnb.Rule_foo_3c2199da53c4480ea0ec7b3d1c4781b5.defaultConsequence(Rule_foo_3c2199da53c4480ea0ec7b3d1c4781b5.java:7) at org.gregcode.mnb.Rule_foo_3c2199da53c4480ea0ec7b3d1c4781b5DefaultConsequenceInvokerGenerated.evaluate(Unknown Source) at org.gregcode.mnb.Rule_foo_3c2199da53c4480ea0ec7b3d1c4781b5DefaultConsequenceInvoker.evaluate(Unknown Source) at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:1091) "MonkeyWrapper" is not in my code, so I'm assuming it's generated. I also tried creating a HungryMonkey and HungryMonkeyImpl interface/class pair like the Scholar and ScholarImpl from the traits example, but the same exception happened. Any clues?