[WORKAROUND] Prevent exception while using EXT:container upgrade wizard

There are some reported cases, that an exception occurs, if the upgrade
wizard "Migrate container sorting" of EXT:container is executed.

Resolves: #988

Classes/EventListener/FlexFormParsingModifyEventListener.php

@@ -77,13 +77,16 @@ protected function getSheetNameAndRemoveFromConfiguration(array &$configuration)
 
     private function getPidForCurrentRecord(): int
     {
+        $uid = 0;
         $request = $this->getRequest();
-        $queryParams = $request->getQueryParams();
-        $uid = array_keys($queryParams['edit']['tt_content'] ?? [])[0] ?? 0;
+        if ($request) {
+            $queryParams = $request->getQueryParams();
+            $uid = array_keys($queryParams['edit']['tt_content'] ?? [])[0] ?? 0;
+        }
         return DatabaseUtility::getPidForRecord($uid, 'tt_content');
     }
 
-    private function getRequest(): ServerRequestInterface
+    private function getRequest(): ?ServerRequestInterface
     {
         return $GLOBALS['TYPO3_REQUEST'];
     }