API 2.0: Updates to Epics are not allowed if the Theme is inactive/deleted, nor if the owner is inactive

Issue Summary

When trying to update an Epic through the API (be it a PATCH/PUT) it will throw an error if the Theme associated with it is inactive or deleted, the same if the owner is not active anymore. The problem is that the UI allows updates in both cases.

Steps to Reproduce

1. Create a Theme
2. Create an Epic
3. Associate the Epic with the Theme
4. On the Theme, mark Active as No (or delete it)
5. Try to update the Epic title thru the UI
6. Try to update the same thing thru API
   The same test goes with the owner/user.

Expected Results

TBD by the Product team

Actual Results

The UI allows the update but the API doesn't.

Workaround

Currently, there is no known workaround for this behavior. A workaround will be added here when available