minor #8541 Doctrine event listener could persist a null value (matt9mg)

This PR was submitted for the 3.3 branch but it was merged into the 2.7 branch instead (closes #8541).

Discussion
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Doctrine event listener could persist a null value

In the current docs, say the entity name is updated and we have not uploaded a new file, it looks like the fileName would be null meaning if the entity already has a brochure it would be removed?

Commits
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713f382 Doctrine event listener could persist a null value

Author: xabbuh

controller/upload_file.rst

@@ -365,9 +365,8 @@ automatically upload the file when persisting the entity::
             // only upload new files
             if ($file instanceof UploadedFile) {
                 $fileName = $this->uploader->upload($file);
+                $entity->setBrochure($fileName);
             }
-
-            $entity->setBrochure($fileName);
         }
     }