Description of problem:
When I add a DataObject to a process and let the designer generate the assignments and datasets (by saving the process and opening it) then this DataObject cannot be removed. If I remove it and save the process then any subsequent attempt to open the file will fail.

How to reproduce:
1) create a process
2) add start->task->end
3) add a DataObject and connect it to the task
4) save, close and open the process
5) remove the DataObject
6) save, close and attempt to open

Actual result:
Error message is shown (attached screenshot)

Expected result:
The process will open

Additional info:
See attached screencast