NPE during Process Migration when Boundary Timer is fired but UserTask not completed

Community issue:

_I have boundary timer events attached to the human tasks. Following are the scenarios
1) I am having this particular issue with the process instance migration when the attached boundary timer event is triggered and completed but not the human task( Human task is still active).
2) No issue with process instance migration when both human task and its attached boundary timer events are completed._

https://groups.google.com/forum/#!topic/jbpm-usage/QjLeuJ8_EtM