I am getting the following error when trying to insert my object into ksession. I have attached my rules and java object. Please help me in debugging why this is happening. I am using java 5 and drools 5.0

thanks

error while inserting:

org.drools.RuntimeDroolsException:
defaultpkg.Rule_CheckStationNumber_0Eval0Invoker@e4aea391 : java.lang.NullPointerException

rules.drl
import java.lang.*;
import java.util.*;
import ct.fw.rules.*;
import ct.fw.utils.*;
import ct.fw.rules.*;
import ct.fw.logging.*;
import ct.fw.pf.dbi.*;
import ct.fw.pf.dao.*;
import ct.fw.pf.seq.*;
import ct.fw.pf.util.*;
import ct.fw.pf.vo.*;
import ct.fw.ex.*;
import org.apache.commons.lang.*;
import com.aa.gccp.domain.*;

   global ct.fw.rules.AssertionObject ao
   global ct.fw.logging.SmartLogger log

    function BillingRecord getRecord(AssertionObject ao)
        {
            return (BillingRecord) ao.get(0);
        }
    function void debug(String msg,SmartLogger log)
        {
            log.debug(BusinessRulesValidator.class, msg);
        }
    function void error(String msg,SmartLogger log)
        {
            log.error(BusinessRulesValidator.class, msg);
            System.out.println("Message from rules "+msg);
        }

rule CheckTrue
when
   eval(true)
then
    System.out.println("evaluating true");
end

rule CheckTrue2
when
   eval(true)
then
    error("evaluating from rules2",log);
end

rule CheckStationNumber
when
   eval(((getRecord(ao)).getStationNo()) == null)
then
    error("station number should not be null",log);
end

part where i load the rules and insert the facts. There is no error when loading the rules.drl. That means no parsing errors. The error happens at ksessio.insert(assertionObject).

public void assertRulesObject(AssertionObject assertionObject) throws BusinessRuleException
    {
        long current = System.currentTimeMillis();
        KnowledgeBase kbase = knowledgeBasesMap.get(rulesFileName);

        if (kbase == null)
        {
            kbase = knowledgeBasesMap.get(rulesFileName + DRL);
        }

        if ((kbase == null) || ((current - lastRefreshedMilliseconds) > refreshTimeMilliseconds))
        {
            if (rulesFileName.toLowerCase().indexOf(DRL) == -1)
            {
                kbase = load(rulesFileName + DRL);
            }
            else
            {
                kbase = load(rulesFileName);
            }

            lastRefreshedMilliseconds = System.currentTimeMillis();
        }
        this.assertionObject = assertionObject;

        List assertionobjectslist = new ArrayList();
// i am just doing this part just to make sure assertion object is not null and i will get some answer. this part runs fine.
if (assertionObject != null)
        {
            assertionobjectslist = assertionObject.getValidationObjects();
            String StationNumber = ((BillingRecord) assertionObject.get(0)).getStationNo();
            System.out.println("Station Number in assertion object is " + StationNumber);
        }
        else
        {
            System.out.println("Assertion Object is null");
        }
        System.out.println("The number of objects in assertionobject is " + assertionobjectslist.size());

        try
        {
            StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();
//the next line throws the exception
            ksession.insert(assertionObject);

            ksession.fireAllRules();
            ksession.dispose();

        }
        catch (RuntimeDroolsException e1)
        {
            throw new BusinessRuleException(e1.getMessage());
        }

        businessRulesErrors = assertionObject.getBusinessRulesErrors();

        if (throwException)
        {
            if (!assertionObject.getBusinessRulesErrors().isEmpty())
            {
                throw new BusinessRuleException(businessRulesErrors);
            }
        }
    }

Any help is appreciated. thanks