diff --git a/src/plugin/announcement/Entity/Announcement.php b/src/plugin/announcement/Entity/Announcement.php
index 49946ede921..3ed1b48e2b7 100644
--- a/src/plugin/announcement/Entity/Announcement.php
+++ b/src/plugin/announcement/Entity/Announcement.php
@@ -305,7 +305,7 @@ public function getCreator()
     /**
      * Set creator.
      */
-    public function setCreator(User $creator)
+    public function setCreator(?User $creator = null)
     {
         $this->creator = $creator;
     }
diff --git a/src/plugin/forum/Subscriber/Crud/SubjectSubscriber.php b/src/plugin/forum/Subscriber/Crud/SubjectSubscriber.php
index 1de2e1dc91d..6c9ae910405 100644
--- a/src/plugin/forum/Subscriber/Crud/SubjectSubscriber.php
+++ b/src/plugin/forum/Subscriber/Crud/SubjectSubscriber.php
@@ -74,15 +74,17 @@ public function preCreate(CreateEvent $event)
         $forum = $subject->getForum();
 
         //create user if not here
-        $user = $this->om->getRepository(UserValidation::class)->findOneBy([
-            'user' => $subject->getCreator(),
-            'forum' => $forum,
-        ]);
-
-        if (!$user) {
-            $user = new UserValidation();
-            $user->setForum($forum);
-            $user->setUser($subject->getCreator());
+        if ($subject->getCreator()) {
+            $user = $this->om->getRepository(UserValidation::class)->findOneBy([
+                'user' => $subject->getCreator(),
+                'forum' => $forum,
+            ]);
+
+            if (!$user) {
+                $user = new UserValidation();
+                $user->setForum($forum);
+                $user->setUser($subject->getCreator());
+            }
         }
 
         $messages = $subject->getMessages();