Comment 11 for bug 580218

You are right - there are 2 issues
* xml definitions do not allow to "delete" context (and probably other) fields
* this leads to the need to do manual updates

your proposed solution "mandatory" does not give any positive feedback what to do if the field is set to None.

the admin has to "know" that at least '{}' has to be entered. I doubt that all admins will know or guess.

probably the logic could/should be changed to handle empty fields gracefully.

I also doubt slightly that the help text (currently missing) will be consulted in case of mandatory error.