add typehints and return types

src/Provider/NodeProviderInterface.php

@@ -25,7 +25,7 @@ interface NodeProviderInterface
     /**
      * Returns the system node ID
      *
-     * @return string System node ID as a hexadecimal string
+     * @return string|null|false System node ID as a hexadecimal string
      * @throws Exception if it was not possible to gather sufficient entropy
      */
     public function getNode();