diff --git a/typo3/sysext/frontend/Classes/ContentObject/Menu/AbstractMenuContentObject.php b/typo3/sysext/frontend/Classes/ContentObject/Menu/AbstractMenuContentObject.php
index 5a9be41ca04b250268a6a0a0071331348ad7f4ae..80982c1a81f2c9d2d908f5cbd102bf64097092e8 100644
--- a/typo3/sysext/frontend/Classes/ContentObject/Menu/AbstractMenuContentObject.php
+++ b/typo3/sysext/frontend/Classes/ContentObject/Menu/AbstractMenuContentObject.php
@@ -1809,9 +1809,10 @@ abstract class AbstractMenuContentObject
                 );
             }
             if (is_array($row)) {
-                if ($this->mconf['sectionIndex.']['type'] !== 'all') {
+                $sectionIndexType = $this->mconf['sectionIndex.']['type'] ?? '';
+                if ($sectionIndexType !== 'all') {
                     $doIncludeInSectionIndex = $row['sectionIndex'] >= 1;
-                    $doHeaderCheck = $this->mconf['sectionIndex.']['type'] === 'header';
+                    $doHeaderCheck = $sectionIndexType === 'header';
                     $isValidHeader = ((int)$row['header_layout'] !== 100 || !empty($this->mconf['sectionIndex.']['includeHiddenHeaders'])) && trim($row['header']) !== '';
                     if (!$doIncludeInSectionIndex || ($doHeaderCheck && !$isValidHeader)) {
                         continue;