Set the ``guardian`` to ``NULL`` after user removal.
Set the ``guardian`` to ``NULL`` after user removal.

https://github.com/madewithbytes/us_ignite/issues/152

Allowing nullable ownership by setting the User FK to ``NULL``
on removal.

us-ignite/us_ignite,us-ignite/us_ignite,us-ignite/us_ignite,us-ignite/us_ignite,us-ignite/us_ignite