Call to member function delete() on null

[Robert-Hucks]

There is an issue that occurs whenever a model is deleted from the database and therefore is unretrievable for SelfDestruct. It tries to fetch the model and call delete() on it, but the model fails to return and this leads to the function call failing also, resulting in a huge amount of error logs.

A check needs to be put in place to simply remove the SelfDestruct record if the object it is trying to delete() no longer exists.