Update from 1.11.x

main/inc/lib/message.lib.php

@@ -1116,9 +1116,9 @@ class MessageManager
         $content = Security::remove_XSS($row['content'], STUDENT, true);
 
         $name = get_lang('UnknownUser');
+        $fromUser = api_get_user_info($user_sender_id);
         $userImage = '';
-        if (!empty($user_sender_id)) {
-            $fromUser = api_get_user_info($user_sender_id);
+        if (!empty($user_sender_id) && !empty($fromUser)) {
             $name = $fromUser['complete_name_with_username'];
             $userImage = Display::img(
                 $fromUser['avatar_small'],

main/messages/new_message.php

@@ -73,7 +73,8 @@ function show_compose_reply_to_message($message_id, $receiver_id)
     $result = Database::query($query);
     $row = Database::fetch_array($result, 'ASSOC');
 
-    if (empty($row['user_sender_id'])) {
+    $userInfo = api_get_user_info($row['user_sender_id']);
+    if (empty($row['user_sender_id']) || empty($userInfo)) {
         $html = get_lang('InvalidMessageId');
 
         return $html;