Pushing a job to the queue results in a serialize Closure error

I have opted to use the database queue driver for now. I have a job in app/Jobs/, then in a Controller I have the relavent use statement. Then when I have the line Queue::push(new CheckTopic($url)); I get the following error: “Exception in Queue.php line 91: Serialization of 'Closure' is not allowed”. Here’s the stack trace:

    in Queue.php line 91
    at serialize(object(CheckTopic)) in Queue.php line 91
    at Queue->createPayload(object(CheckTopic), '') in DatabaseQueue.php line 67
    at DatabaseQueue->push(object(CheckTopic))
    at call_user_func_array(array(object(DatabaseQueue), 'push'), array(object(CheckTopic))) in QueueManager.php line 223
    at QueueManager->__call('push', array(object(CheckTopic))) in Facade.php line 210
    at QueueManager->push(object(CheckTopic)) in Facade.php line 210
    at Facade::__callStatic('push', array(object(CheckTopic))) in TopicsController.php line 44
    at Queue::push(object(CheckTopic)) in TopicsController.php line 44
    at TopicsController->update(object(Request)) in HTTPPostController.php line 23
    at HTTPPostController->checkMode(object(Request))
    at call_user_func_array(array(object(HTTPPostController), 'checkMode'), array(object(Request))) in Container.php line 523
    at Container->call(array(object(HTTPPostController), 'checkMode'), array()) in Application.php line 1296
    at Application->callControllerCallable(array(object(HTTPPostController), 'checkMode'), array()) in Application.php line 1261
    at Application->callLumenController(object(HTTPPostController), 'checkMode', array(true, array('uses' => 'App\Http\Controllers\HTTPPostController@checkMode'), array())) in Application.php line 1232
    at Application->callControllerAction(array(true, array('uses' => 'App\Http\Controllers\HTTPPostController@checkMode'), array())) in Application.php line 1200
    at Application->callActionOnArrayBasedRoute(array(true, array('uses' => 'App\Http\Controllers\HTTPPostController@checkMode'), array())) in Application.php line 1185
    at Application->handleArrayBasedFoundRoute(array(true, array('uses' => 'App\Http\Controllers\HTTPPostController@checkMode'), array())) in Application.php line 1163
    at Application->handleFoundRoute(array(true, array('uses' => 'App\Http\Controllers\HTTPPostController@checkMode'), array())) in Application.php line 1090
    at Application->dispatch(null) in Application.php line 1035
    at Application->run() in index.php line 28

Anyone any idea how to fix this?

Just to make sure, I have installed jeremeamia/superclosure and still get the same error.