diff --git a/Classes/Update/PowermailPluginUpdater.php b/Classes/Update/PowermailPluginUpdater.php
index ee8aa0041..da2d0fc2b 100644
--- a/Classes/Update/PowermailPluginUpdater.php
+++ b/Classes/Update/PowermailPluginUpdater.php
@@ -134,7 +134,7 @@ public function performMigration(string $list_type): bool
                 }
             } else {
                 $targetCType = 'powermail_pi1';
-                $newFlexform = $record['pi_flexform'];
+                $newFlexform = $record['pi_flexform'] ?? '';
             }
 
             // Remove flexform data which do not exist in flexform of new plugin