diff --git a/typo3/sysext/backend/Classes/Controller/ContentElement/NewContentElementController.php b/typo3/sysext/backend/Classes/Controller/ContentElement/NewContentElementController.php
index e0845001c014b77d20509b6e0115db2405ecb636..4770e0fa0627c520ba5b25336d7eadac6f4b4c57 100644
--- a/typo3/sysext/backend/Classes/Controller/ContentElement/NewContentElementController.php
+++ b/typo3/sysext/backend/Classes/Controller/ContentElement/NewContentElementController.php
@@ -455,7 +455,7 @@ class NewContentElementController
     protected function getWizardGroupHeader(array $wizardGroup): array
     {
         return [
-            'header' => $this->getLanguageService()->sL($wizardGroup['header'])
+            'header' => $this->getLanguageService()->sL($wizardGroup['header'] ?? '')
         ];
     }
 
diff --git a/typo3/sysext/backend/Classes/Form/Container/FlexFormElementContainer.php b/typo3/sysext/backend/Classes/Form/Container/FlexFormElementContainer.php
index 0e1dc03f4661ddd108c3a2e488b079cc55745545..a6da15f61c2bc614b3827120d12facbf78302dbd 100644
--- a/typo3/sysext/backend/Classes/Form/Container/FlexFormElementContainer.php
+++ b/typo3/sysext/backend/Classes/Form/Container/FlexFormElementContainer.php
@@ -74,8 +74,8 @@ class FlexFormElementContainer extends AbstractContainer
                 // Set up options for single element
                 $fakeParameterArray = [
                     'fieldConf' => [
-                        'label' => $languageService->sL(trim($flexFormFieldArray['label'])),
-                        'config' => $flexFormFieldArray['config'],
+                        'label' => $languageService->sL(trim($flexFormFieldArray['label'] ?? '')),
+                        'config' => $flexFormFieldArray['config'] ?? [],
                         'children' => $flexFormFieldArray['children'] ?? [],
                         'onChange' => $flexFormFieldArray['onChange'] ?? '',
                     ],
diff --git a/typo3/sysext/extbase/Classes/Persistence/Generic/Mapper/DataMapFactory.php b/typo3/sysext/extbase/Classes/Persistence/Generic/Mapper/DataMapFactory.php
index c42e46d9e50231734704d6857537871b94f1082a..0e95bfbebf2cc198821e62deae4e285b31f928d6 100644
--- a/typo3/sysext/extbase/Classes/Persistence/Generic/Mapper/DataMapFactory.php
+++ b/typo3/sysext/extbase/Classes/Persistence/Generic/Mapper/DataMapFactory.php
@@ -367,7 +367,10 @@ class DataMapFactory implements SingletonInterface
         // todo: take place outside this method.
 
         $columnMap->setTypeOfRelation(ColumnMap::RELATION_HAS_ONE);
-        $columnMap->setChildTableName($columnConfiguration['foreign_table']);
+        // check if foreign_table is set, which usually won't be the case for type "group" fields
+        if (!empty($columnConfiguration['foreign_table'])) {
+            $columnMap->setChildTableName($columnConfiguration['foreign_table']);
+        }
         // todo: don't update column map if value(s) isn't/aren't set.
         $columnMap->setChildSortByFieldName($columnConfiguration['foreign_sortby'] ?? null);
         $columnMap->setParentKeyFieldName($columnConfiguration['foreign_field'] ?? null);
@@ -392,12 +395,15 @@ class DataMapFactory implements SingletonInterface
         // todo: take place outside this method.
 
         $columnMap->setTypeOfRelation(ColumnMap::RELATION_HAS_MANY);
-        $columnMap->setChildTableName($columnConfiguration['foreign_table']);
+        // check if foreign_table is set, which usually won't be the case for type "group" fields
+        if (!empty($columnConfiguration['foreign_table'])) {
+            $columnMap->setChildTableName($columnConfiguration['foreign_table']);
+        }
         // todo: don't update column map if value(s) isn't/aren't set.
         $columnMap->setChildSortByFieldName($columnConfiguration['foreign_sortby'] ?? null);
         $columnMap->setParentKeyFieldName($columnConfiguration['foreign_field'] ?? null);
         $columnMap->setParentTableFieldName($columnConfiguration['foreign_table_field'] ?? null);
-        if (is_array($columnConfiguration['foreign_match_fields'] ?? null)) {
+        if (isset($columnConfiguration['foreign_match_fields']) && is_array($columnConfiguration['foreign_match_fields'])) {
             $columnMap->setRelationTableMatchFields($columnConfiguration['foreign_match_fields']);
         }
         return $columnMap;
diff --git a/typo3/sysext/opendocs/Classes/Controller/OpenDocumentController.php b/typo3/sysext/opendocs/Classes/Controller/OpenDocumentController.php
index 9ee5cd8b4d04bdfd0d4734b402c715da48bc7acb..889f57fb3df4f2e6bf8f6e1ac444d920b6503946 100644
--- a/typo3/sysext/opendocs/Classes/Controller/OpenDocumentController.php
+++ b/typo3/sysext/opendocs/Classes/Controller/OpenDocumentController.php
@@ -69,7 +69,7 @@ class OpenDocumentController
      */
     public function closeDocument(ServerRequestInterface $request): ResponseInterface
     {
-        $identifier = $request->getParsedBody()['md5sum'] ?? $request->getQueryParams()['md5sum'];
+        $identifier = $request->getParsedBody()['md5sum'] ?? $request->getQueryParams()['md5sum'] ?? null;
 
         if ($identifier) {
             $this->documents->closeDocument($identifier);