Remove nullable types from two arguments

Since we have default `null` values already, they do not need to be
reported as nullable to allow a `null` value to be passed.

Author: weierophinney

src/UrlHelper.php

@@ -37,10 +37,10 @@ public function __construct(BaseHelper $helper)
      * @return string
      */
     public function __invoke(
-        ?string $routeName = null,
+        string $routeName = null,
         array $routeParams = [],
         array $queryParams = [],
-        ?string $fragmentIdentifier = null,
+        string $fragmentIdentifier = null,
         array $options = []
     ) {
         return $this->helper->generate($routeName, $routeParams, $queryParams, $fragmentIdentifier, $options);