[BUGFIX] The layout source is returning null, but must be of type Layout

Classes/Service/MailTemplateService.php

@@ -1028,9 +1028,9 @@ class MailTemplateService {
 	 *
 	 * @param int $layoutUid
 	 * @param int $siteRootId
-	 * @return Layout
+	 * @return Layout|NULL
 	 */
-	private function getLayoutSource(int $layoutUid, int $siteRootId): Layout {
+	private function getLayoutSource(int $layoutUid, int $siteRootId): ?Layout {
 		$languageUid = 0;
 		if ($this->language !== self::DEFAULT_LANGUAGE) {
 			$languageUid = (int) array_search($this->language, $this->getAvailableLanguages(), TRUE);