[rules-users] Problems with condition Rules

I'm using JBoos Drools 3.0. I'm using Java 5 I have the following classes package org.unlp.model; import java.util.ArrayList; import java.util.List; /** * @author Jvelilla * */ public class Curso { ... // describe el numero total de cuotas del curso protected Integer cuotas; // Un curso de postgrado tiene una lista de materias protected List<Materia> materias; // ~ Constructors ================================================ ... // ~ Methods ================================================ public void setCuotas(Integer cuotas) { this.cuotas = cuotas; } ... public Integer getCuotas() { return cuotas; } ... } package org.unlp.model; /** * @author Jvelilla * */ public class Estudiante extends Persona { // restriccion un estudiante solo se puede // inscribir en un curso. // ejemplo: Mg. en Ingenieria de Sotware protected Curso inscripcion; protected int cuotasPagas; //~ Methods ================================================ public void setInscripcion(Curso inscripcion) { this.inscripcion = inscripcion; } public void setNumero(int numero) { this.numero = numero; } public void setCuotasPagas(int cuotas_pagas) { this.cuotasPagas = cuotas_pagas; } public Curso getInscripcion() { return inscripcion; } public int getCuotasPagas() { return cuotasPagas; } } My Rule is #created on: 13/08/2006 package org.unlp.model #list any import classes here. import org.unlp.model.Estudiante; #declare any global variables here rule "Descuento por pago al contado" when alumno : Estudiante (cuota : cuotasPagas, x: inscripcion -> ( x.getCuotas().intValue() > cuota.intValue() ) ) then System.out.println( "El alumno: [" + alumno.getNombre()+ "] recibira un descuento por pago al contado del 25%"); System.out.println( "La cantindad de cuotas es [" + alumno.getCuotasPagas()+ "] "); end But I obtain the followin error org.drools.RuntimeDroolsException: java.lang.NullPointerException at org.drools.rule.PredicateConstraint.isAllowed(Unknown Source) at org.drools.common.BetaNodeBinder.isAllowed(Unknown Source) at org.drools.reteoo.LeftInputAdapterNode.assertObject(Unknown Source) at org.drools.reteoo.ObjectSource.propagateAssertObject(Unknown Source) at org.drools.reteoo.ObjectTypeNode.assertObject(Unknown Source) at org.drools.reteoo.Rete.assertObject(Unknown Source) at org.drools.reteoo.ReteooRuleBase.assertObject(Unknown Source) at org.drools.reteoo.ReteooWorkingMemory.doAssertObject(Unknown Source) at org.drools.common.AbstractWorkingMemory.assertObject(Unknown Source) at org.drools.common.AbstractWorkingMemory.assertObject(Unknown Source) at org.unlp.model.BusinessRulesTest.main(BusinessRulesTest.java:45) Caused by: java.lang.NullPointerException at org.unlp.model.Rule_Descuento_por_pago_al_contado_0Predicate0Invoker.evaluate (Rule_Descuento_por_pago_al_contado_0Predicate0Invoker.java:13) ... 11 more What do you suggest I do ? -- "Component design should be the Formula-1 racing of software engineering." Bertrand Meyer