You'll probably need to ensure the String object contains a valid object reference and not a null.
 
If the database allows NULL values on a field then the String object will be set to a null causing the problem you explain. An alternative is to either set the String to an empty String ("") instead of null or change your rule to first check whether the String is a null; for example beanObject.getName() != null && beanObject.getName()=="smurf".

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Mahantesh
Sent: 29 January 2007 08:58
To: rules-users@lists.jboss.org
Subject: [rules-users] required some input on String comparision in xml rulefile.

Hi,

I am using Drools 3 JBoss Rule Engine and xml file as a rule file. when i am using integer condition in LHS part of rule file it is working fine.
For example:  <eval> beanObject.getNumber >= 60 </eval>

but when using  string condition in LHS part of the rule file, it is able to filter the data when setting and getting the data from the dummy bean, but not able to filter the data when the data is coming from the database its throwing the exceptions like this.

For Example: <eval> beanObject.getName()</eval>

Exception like this.

org.drools.RuntimeDroolsExcept
ion: java.lang.NullPointerException
       at org.drools.rule.EvalCondition.isAllowed (Unknown Source)
       at org.drools.reteoo.EvalConditionNode.assertTuple(Unknown Source)
       at org.drools.reteoo.TupleSource.propagateAssertTuple(Unknown Source)
       at org.drools.reteoo.JoinNode.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.drools.jsr94.rules.StatelessRuleSessionImpl.executeRules(Unknown Source)
       at org.drools.jsr94.rules.StatelessRuleSessionImpl.executeRules (Unknown Source)
       at rules1.TestRuleForXML.applyRuleTestingProcessVO(TestRuleForXML.java:176)
       at rules1.TestRuleForXML.applyForProcessVO(TestRuleForXML.java:55)
size of the ouput list in  java file: 0

       at rules1.TestRuleForXML.main(TestRuleForXML.java:47)
Caused by: java.lang.NullPointerException
       at rules1.Rule_my_rule_0.eval0(Rule_my_rule_0.java:12)
       at rules1.Rule_my_rule_0Eval0Invoker.evaluate (Rule_my_rule_0Eval0Invoker.java:19)

If you do a help regarding how to work with String condition in LHS part, it will be great..

Thanks in Advance,
Mahantesh.