Resolve #3441923 "Use xxhash"

Closes #3441923

automatic_updates_extensions/src/Form/UpdateReady.php

@@ -94,7 +94,7 @@ final class UpdateReady extends UpdateFormBase {
   /**
    * {@inheritdoc}
    */
-  public function buildForm(array $form, FormStateInterface $form_state, string $stage_id = NULL) {
+  public function buildForm(array $form, FormStateInterface $form_state, ?string $stage_id = NULL) {
     try {
       $this->stage->claim($stage_id);
     }