diff --git a/typo3/sysext/core/Classes/Authentication/AbstractUserAuthentication.php b/typo3/sysext/core/Classes/Authentication/AbstractUserAuthentication.php
index 960c750379a4209e1a7a5c07f0da614b516cf6c7..b392f436b97eca95a48731190bf076f18e49ef8b 100644
--- a/typo3/sysext/core/Classes/Authentication/AbstractUserAuthentication.php
+++ b/typo3/sysext/core/Classes/Authentication/AbstractUserAuthentication.php
@@ -352,7 +352,7 @@ abstract class AbstractUserAuthentication implements LoggerAwareInterface
     protected function getCookieDomain()
     {
         $result = '';
-        $cookieDomain = $GLOBALS['TYPO3_CONF_VARS']['SYS']['cookieDomain'];
+        $cookieDomain = $GLOBALS['TYPO3_CONF_VARS']['SYS']['cookieDomain'] ?? '';
         // If a specific cookie domain is defined for a given application type, use that domain
         if (!empty($GLOBALS['TYPO3_CONF_VARS'][$this->loginType]['cookieDomain'])) {
             $cookieDomain = $GLOBALS['TYPO3_CONF_VARS'][$this->loginType]['cookieDomain'];