respect null driver

Author: taylorotwell

src/Illuminate/Queue/QueueServiceProvider.php

@@ -235,6 +235,10 @@ protected function registerFailedJobServices()
         $this->app->singleton('queue.failer', function ($app) {
             $config = $app['config']['queue.failed'];
 
+            if (! isset($config['driver']) || $config['driver'] === 'null') {
+                return new NullFailedJobProvider;
+            }
+
             if (isset($config['driver']) && $config['driver'] === 'dynamodb') {
                 return $this->dynamoFailedJobProvider($config);
             } elseif (isset($config['driver']) && $config['driver'] === 'database-uuids') {