fix undefined index AbstractException

extension/Classes/Core/Exception/AbstractException.php

@@ -171,6 +171,7 @@ class AbstractException extends \Exception {
                 }
 
                 // Render inline report editor
+                $arrMerged[ERROR_MESSAGE_TO_DEVELOPER] = $arrMerged[ERROR_MESSAGE_TO_DEVELOPER] ?? '';
                 try {
                     $arrMerged[ERROR_MESSAGE_TO_DEVELOPER] = QuickFormQuery::buildInlineReport(\UserReportException::$report_uid,
                             \UserReportException::$report_pathFileName,  \UserReportException::$report_bodytext,