Issue #3181367 by longwave, Kristen Pol: TwigEnvironment $loader argument cannot be NULL

core/lib/Drupal/Core/Template/TwigEnvironment.php

@@ -66,7 +66,7 @@ class TwigEnvironment extends Environment {
    * @param array $options
    *   The options for the Twig environment.
    */
-  public function __construct($root, CacheBackendInterface $cache, $twig_extension_hash, StateInterface $state, LoaderInterface $loader = NULL, array $options = []) {
+  public function __construct($root, CacheBackendInterface $cache, $twig_extension_hash, StateInterface $state, LoaderInterface $loader, array $options = []) {
     $this->state = $state;
 
     $this->templateClasses = [];