I have successfully used DRLParser with several DRL files, except when they include the 'contains' syntax. My code for parsing DRL and then dumping into XML, is below: public class DroolsDumper { public static final void main(String[] args) throws DroolsParserException { DrlParser parser = new DrlParser(); PackageDescr descr = parser.parse(new InputStreamReader(DroolsDumper.class.getResourceAsStream("/source.drl" ))); // Dump to xml rule. XmlDumper dumper = new XmlDumper(); String result = dumper.dump(descr); System.out.println(result); }} This code returns the following error when the DRL includes 'contains' syntax: Exception in thread "main" java.lang.NullPointerException at org.drools.xml.XmlDumper.visitPackageDescr(XmlDumper.java:224) at org.drools.xml.XmlDumper.dump(XmlDumper.java:71) at com.sample.DroolsDumper.main(DroolsDumper.java:19) This code works fine with the following DRL (whether I dump the parsed DRL into XML or back into DRL): rule 'cart rule' dialect "mvel" when Cart () then System.out.println("Hello World"); end But it returns the above error when the same DRL includes 'contains': rule 'cart rule' dialect "mvel" when Cart (skus contains (123)) then System.out.println("Hello World"); end The DRL works fine in test scenarios and my cart class's array is declared simply as follows: package shopping; import java.util.ArrayList; public class Cart { public ArrayList<Integer> skus = new ArrayList<Integer>(); public ArrayList<Integer> getSkus() { return skus; } public void setSkus(ArrayList<Integer> skus) { this.skus = skus; } }