public function deleted(UserInvitation $invitation)
    {
        // Insert into 'revisions' (calling getTable probably not necessary, but to be safe).
        \DB::table((new Revision())->getTable())->insert([
            [
                'revisionable_type' => $invitation->getMorphClass(),
                'revisionable_id' => $invitation->id,
                'key' => 'deleted_at',
                'old_value' => null,
                'new_value' => new \DateTime(),
                'user_id' => (\Auth::check() ? \Auth::user()->id : null),
                'created_at' => new \DateTime(),
                'updated_at' => new \DateTime(),
            ]
        ]);
    }