I am trying to exceute human task example given at https://github.com/droolsjbpm/jbpm/tree/master/jbpm-examples/src/main/java/org/jbpm/examples/humantask.

Sometimes it run correctly and giving following output:

Sales-rep executing task Request Review(13: null)
krisv executing task Request Approval(18: null)
john executing task Request Approval(17: null)
sales-rep executing task Request Reminder(14: null)
result = Accept
ActorId = sales-rep
description = Need a new laptop computer
userId = krisv
TaskName = Request Reminder
date = Fri Sep 09 10:47:40 IST 2011
comment = Agreed, existing laptop needs replacing

But if I trying to debug it or run it normally,sometimes it gives output mentioned below:

Sales-rep executing task Request Review(8: null)
java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
          at java.util.ArrayList.RangeCheck(ArrayList.java:547)
          at java.util.ArrayList.get(ArrayList.java:322)
          at org.jbpm.examples.humantask.HumanTaskExample.main(HumanTaskExample.java:94)

I can't able to understand this behaviour of program. Why this is happening? Is it related with time gap or what?