Activiti shows "An unknown error occurred" instead of known error message
This user will then see the error on the Share UI popup.
An example would be to have `throw ("Hello, world!")` and the popup will display something like the following:
It was previously working in ACS 5.1.2, but since the upgrade to 6.2.2, it only worked for the start task (which uses execution listener), while all other tasks show the following message:
Steps to reproduce:
1. Download the built-in Activiti adhoc.bpmn20.xml workflow from activiti-admin
2. Add the following code into <startEvent> element to throw an error when message is empty
3. Add the following code to throw an error in the "adhocTask" user task under the <extensionElements> element
4. Upload the new adhoc.bpmn20.xml file into activiti admin
5. Log in to Share, go to the start workflow page and select "New Task"
6. set yourself as the "assign to" user, leave the message blank and try to start the workflow
(there should be a pop up that says, "Message cannot be blank!")
7. Fill in the "message" and start the workflow
8. Go to the task that you have been assigned, and click on "Task Done"
Popup should show "This is a known error!"
The popup shows,