diff --git a/src/ApplenewsManager.php b/src/ApplenewsManager.php
index ec49949..4ef10a0 100644
--- a/src/ApplenewsManager.php
+++ b/src/ApplenewsManager.php
@@ -336,7 +336,7 @@ class ApplenewsManager {
    *
    * @param array $sections
    *   An array of section ids.
-   * @param string $revision_id
+   * @param null|string $revision_id
    *   Revision ID for article update.
    * @param bool $is_preview
    *   Is the article published as a preview.
@@ -344,7 +344,7 @@ class ApplenewsManager {
    * @return string
    *   JSON metadata string.
    */
-  protected function getMetadata(array $sections, string $revision_id = '', bool $is_preview = FALSE): string {
+  protected function getMetadata(array $sections, $revision_id = NULL, bool $is_preview = FALSE): string {
     foreach ($sections as $section_id => $flag) {
       $section_url = new Uri($this->config->get('endpoint'));
       $section_url = $section_url->withPath('/sections/' . $section_id);