Description of problem:
When I run a simple process with a human task and complete this task in task list, a modal dialog appears with message: Error "Unexpected error encountered : java.lang.NullPointerException". There is no stack trace provided, no exception appears in the server.log.

I have a strong suspicion, that the problem might be caused by some of the ErrorCallbacks added with commit https://github.com/droolsjbpm/jbpm-console-ng/commit/b790a808172beef86909a386078ba57639bd5b77 which now catches an exception, that was previously ignored.

Version-Release number of selected component (if applicable):
BPMS 6.0.1 ER1

How reproducible:
Always

Steps to Reproduce:
1. Define a simplistic process with no process variables and just one human task with assignment defined for user you are logged in with
2. Deploy the project, start process instance, go to task list
3. Complete the task assigned to your user by clicking work (tick icon) and clicking complete button in the Task Details window

Actual results:
Modal dialog withe Error message: "Unexpected error encountered : java.lang.NullPointerException" is displayed.

Expected results:
No error modal displayed.

Additional info:
It happens for several of my processes I used for task assignments. All these processes have one thing in common: they have no forms modeler form associated with human tasks. Do you think it might be the cause of the NPE?