Backlog: Process step filter "doesn't contain"

Issue Summary

Empty process steps are not considered when filtering "doesn't contain" process step.

Steps to Reproduce

1. Create a developmental process step for Epics.
2. Enable Process Steps for that Epic.
3. Create several Epics under that prorgram
4. Navigate to Epic Backlog.
5. Make sure some epics does not have any process steps indicated.
   
6. Set a "doesn't contain" process step filter.
   
7. Check the results

Expected Results

It should also return Epics with empty process steps.

Actual Results

Only considers Epics with process steps values.

Workaround

Make sure not to leave any process steps empty so that they will not be missed out when filtered.