fix null config

src/SenangPayServiceProvider.php

                 'merchant_id' => env('SENANGPAY_MERCHANT_ID'),
                 'secret_key' => env('SENANGPAY_SECRET_KEY'),
             ],
-            $config->get('payment.gateway.senangpay')
+            $config->get('payment.gateway.senangpay', [])
         ));
 
         $this->app->afterResolving('payment', function (PaymentManager $manager) use ($config) {