diff --git a/typo3/sysext/core/Classes/Utility/ExtensionManagementUtility.php b/typo3/sysext/core/Classes/Utility/ExtensionManagementUtility.php
index 5047bd2a911a1ff75e1f3213d327073159fc855a..954160d413cf7190379806d8ed5f17d58b0cca50 100644
--- a/typo3/sysext/core/Classes/Utility/ExtensionManagementUtility.php
+++ b/typo3/sysext/core/Classes/Utility/ExtensionManagementUtility.php
@@ -634,7 +634,7 @@ class ExtensionManagementUtility
      */
     public static function addFieldsToUserSettings($addFields, $insertionPosition = '')
     {
-        $GLOBALS['TYPO3_USER_SETTINGS']['showitem'] = self::executePositionedStringInsertion($GLOBALS['TYPO3_USER_SETTINGS']['showitem'], $addFields, $insertionPosition);
+        $GLOBALS['TYPO3_USER_SETTINGS']['showitem'] = self::executePositionedStringInsertion($GLOBALS['TYPO3_USER_SETTINGS']['showitem'] ?? '', $addFields, $insertionPosition);
     }
 
     /**