diff --git a/src/Contao/Event/Subscriber.php b/src/Contao/Event/Subscriber.php
index 25e30844..8389ac93 100644
--- a/src/Contao/Event/Subscriber.php
+++ b/src/Contao/Event/Subscriber.php
@@ -514,7 +514,7 @@ private static function renderSimpleCheckbox(
     ): void {
         if (
             (null !== $event->getRendered())
-            || !(!((bool) $extra['multiple']) && ('checkbox' === $property->getWidgetType()))
+            || !(!((bool) ($extra['multiple'] ?? false)) && ('checkbox' === $property->getWidgetType()))
         ) {
             return;
         }
diff --git a/src/Controller/Ajax.php b/src/Controller/Ajax.php
index d11c442d..544c4c52 100644
--- a/src/Controller/Ajax.php
+++ b/src/Controller/Ajax.php
@@ -234,6 +234,9 @@ public function executePostActions(DataContainerInterface $container)
         assert($inputProvider instanceof InputProviderInterface);
 
         $action = $inputProvider->getValue('action');
+        if (null === $action) {
+            return;
+        }
 
         if (
             \in_array(