FEATURE: Use created_at to remove an ip if its last_match_at is null

app/jobs/scheduled/clean_up_unmatched_ips.rb

@@ -11,7 +11,7 @@ module Jobs
 
       # remove old unmatched IP addresses
       ScreenedIpAddress.where(action_type: ScreenedIpAddress.actions[:block])
-                       .where("last_match_at < ?", last_match_threshold)
+                       .where("last_match_at < ? OR (last_match_at IS NULL AND created_at < ?)", last_match_threshold, last_match_threshold)
                        .destroy_all
     end