Issue #3243258 by gaurav.kapoor: Getting this error when trying to access the user guide page

src/Controller/OverviewController.php

@@ -101,7 +101,7 @@ class OverviewController extends ControllerBase {
    * @return string
    *   Return string which can be displayed in documentation overview.
    */
-  public function resolveParameter(string $value, mixed $parameters) {
+  public function resolveParameter(string $value, ?array $parameters) {
     $computed_value = '';
     $parts = explode('@parameter', $value);
     foreach ($parts as $k => $v) {