<br>   Seems like a bug and I did fixed a problem that raised NPE in a similar situation a few weeks back in trunk. If you can try trunk and let us know if it still happens, it would be great. Otherwise I will try it myself as soon as I have a chance.<br>
<br>   Thanks,<br>      Edson<br><br><div class="gmail_quote">2009/11/16 richarda <span dir="ltr">&lt;<a href="mailto:richard.ambridge@gmail.com">richard.ambridge@gmail.com</a>&gt;</span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br>
I wish to have a rule that says,  if I get one event, but not another one<br>
after a period, then do something.<br>
But I also want to only do this once..<br>
<br>
So, I wrote the rules: (using the eclipse sample project)<br>
<br>
<br>
<br>
declare Message<br>
        @role( event )<br>
end<br>
<br>
rule &quot;Hello World&quot;<br>
        when<br>
                $m : Message( status == Message.HELLO )<br>
                not ( Message( status== Message.GOODBYE, this after [0s,1m] $m)) ;<br>
        then<br>
                System.out.println( &quot;Hello&quot; );<br>
end<br>
<br>
rule &quot;GoodBye&quot;<br>
        when<br>
                $one : Message( status == Message.HELLO )<br>
                $two : Message( status == Message.HELLO )<br>
        then<br>
                System.out.println( &quot;Two hellos, remove one&quot; );<br>
                retract($two);<br>
end<br>
<br>
<br>
But, when I run;<br>
                        Message message = new Message();<br>
                        message.setMessage(&quot;Hello World&quot;);<br>
                        message.setStatus(Message.HELLO);<br>
                        ksession.insert(message);<br>
<br>
                        Message message2 = new Message();<br>
                        message2.setMessage(&quot;Hello World&quot;);<br>
                        message2.setStatus(Message.HELLO);<br>
                        ksession.insert(message2);<br>
                        ksession.fireAllRules();<br>
<br>
I get:<br>
Two hellos, remove one<br>
java.lang.NullPointerException<br>
        at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:970)<br>
        at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:885)<br>
        at org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1086)<br>
        at<br>
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:660)<br>
        at<br>
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:627)<br>
        at<br>
org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:183)<br>
        at com.sample.DroolsTest.main(DroolsTest.java:38)<br>
<br>
<br>
What am i doing wrong?<br>
<font color="#888888">--<br>
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</font></blockquote></div><br><br clear="all"><br>-- <br>  Edson Tirelli<br>  JBoss Drools Core Development<br>  JBoss by Red Hat @ <a href="http://www.jboss.com">www.jboss.com</a><br>