diff --git a/typo3/sysext/workspaces/Classes/Controller/PreviewController.php b/typo3/sysext/workspaces/Classes/Controller/PreviewController.php
index 08cec3d4a71b75db6047a53361141c78069731fb..242a770ee7fc4df17b2ff6bf8a4b52c320bbd5b7 100644
--- a/typo3/sysext/workspaces/Classes/Controller/PreviewController.php
+++ b/typo3/sysext/workspaces/Classes/Controller/PreviewController.php
@@ -203,10 +203,10 @@ class PreviewController
             'enablePreviousStageButton' => $this->isValidStage($previousStage),
             'enableNextStageButton' => $this->isValidStage($nextStage),
             'enableDiscardStageButton' => $this->isValidStage($nextStage) || $this->isValidStage($previousStage),
-            'nextStage' => $nextStage['title'],
-            'nextStageId' => $nextStage['uid'],
-            'prevStage' => $previousStage['title'],
-            'prevStageId' => $previousStage['uid'],
+            'nextStage' => $nextStage['title'] ?? '',
+            'nextStageId' => $nextStage['uid'] ?? 0,
+            'prevStage' => $previousStage['title'] ?? '',
+            'prevStageId' => $previousStage['uid'] ?? 0,
         ]);
 
         $this->moduleTemplate->setContent($this->view->render());
diff --git a/typo3/sysext/workspaces/Classes/Service/StagesService.php b/typo3/sysext/workspaces/Classes/Service/StagesService.php
index d781bba8e7f19d665f20dbf352467b49942dfd77..f01bd855784c70ae254ebcf1fca019cc21cc3139 100644
--- a/typo3/sysext/workspaces/Classes/Service/StagesService.php
+++ b/typo3/sysext/workspaces/Classes/Service/StagesService.php
@@ -94,7 +94,7 @@ class StagesService implements SingletonInterface
                 continue;
             }
             foreach ($items as $item) {
-                $usedStages[$item['t3ver_stage']] = true;
+                $usedStages[$item['t3ver_stage'] ?? 0] = true;
             }
         }
         foreach ($availableStagesForWS as $stage) {
@@ -105,7 +105,7 @@ class StagesService implements SingletonInterface
             }
         }
         foreach ($availableStagesForWSUser as $userWS) {
-            if ($previousStage['uid'] == $userWS['uid']) {
+            if ($previousStage && $previousStage['uid'] == $userWS['uid']) {
                 $found = true;
                 break;
             }
@@ -142,7 +142,7 @@ class StagesService implements SingletonInterface
                 continue;
             }
             foreach ($items as $item) {
-                $usedStages[$item['t3ver_stage']] = true;
+                $usedStages[$item['t3ver_stage'] ?? 0] = true;
             }
         }
         foreach ($availableStagesForWS as $stage) {