fix null config

src/RazerPayServiceProvider.php

                 'verify_key' => env('RAZER_VERIFY_KEY'),
                 'secret_key' => env('RAZER_SECRET_KEY'),
             ],
-            $config->get('payment.gateway.razerpay')
+            $config->get('payment.gateway.razerpay', [])
         ));
 
         $this->app->afterResolving('payment', function (PaymentManager $manager) use ($config) {