[5.4] fixing weird behaviour of Connection method (#18356)

* laravel/framework#18209
implementing fix proposed on the issue

* Update Connection.php

Connection.php

@@ -957,10 +957,10 @@ public function getName()
     /**
      * Get an option from the configuration options.
      *
-     * @param  string  $option
+     * @param  string|null  $option
      * @return mixed
      */
-    public function getConfig($option)
+    public function getConfig($option = null)
     {
         return Arr::get($this->config, $option);
     }