Given an enum Fruit { CHERRY, STRAWBERRY } a rule with a typo in an enum name Jam( fruit == Fruit.CHERIE || == Fruit.STRAWBERRY,... ) causes the NPE shown below while adding the DRL resource: Exception in thread "main" java.lang.NullPointerException at org.drools.rule.AbstractCompositeRestriction.getRequiredDeclarations(AbstractCompositeRestriction.java:59) at org.drools.rule.MultiRestrictionFieldConstraint.getRequiredDeclarations(MultiRestrictionFieldConstraint.java:73) at org.drools.rule.Pattern.setConstraintType(Pattern.java:358) at org.drools.rule.Pattern.addConstraint(Pattern.java:226) at org.drools.rule.builder.PatternBuilder.build(PatternBuilder.java:432) at org.drools.rule.builder.PatternBuilder.buildConstraint(PatternBuilder.java:264) at org.drools.rule.builder.PatternBuilder.build(PatternBuilder.java:213) at org.drools.rule.builder.PatternBuilder.build(PatternBuilder.java:108) at org.drools.rule.builder.GroupElementBuilder.build(GroupElementBuilder.java:69) at org.drools.rule.builder.RuleBuilder.build(RuleBuilder.java:79) at org.drools.compiler.PackageBuilder.addRule(PackageBuilder.java:1151) at org.drools.compiler.PackageBuilder.addPackage(PackageBuilder.java:637) at org.drools.compiler.PackageBuilder.addPackageFromDrl(PackageBuilder.java:267) at org.drools.compiler.PackageBuilder.addKnowledgeResource(PackageBuilder.java:459) at org.drools.builder.impl.KnowledgeBuilderImpl.add(KnowledgeBuilderImpl.java:28) at rss.checker.engine.impl.DroolsEngine.loadSourceRules(DroolsEngine.java:49) at rss.checker.init.Main.exec(Main.java:36) at rss.checker.init.Main.main(Main.java:63)