Fixed broken `null` check for attachment thumbnail links

diff --git a/wcfsetup/install/files/lib/data/attachment/Attachment.class.php b/wcfsetup/install/files/lib/data/attachment/Attachment.class.php
index 163655410514cc03c50797e5927f8f48237b684d..32d9495a1a2c71ed62933427d6520c5a6ef86013 100644 (file)
--- a/wcfsetup/install/files/lib/data/attachment/Attachment.class.php
+++ b/wcfsetup/install/files/lib/data/attachment/Attachment.class.php
@@ -260,7 +260,7 @@ class Attachment extends DatabaseObject implements ILinkableObject, IRouteContro
         }
 
         $thumbnail = $file->getThumbnail($size !== 'tiny' ? '' : $size);
-        if ($this === null) {
+        if ($thumbnail === null) {
             return '';
         }