diff --git a/framework/core/src/Formatter/Formatter.php b/framework/core/src/Formatter/Formatter.php
index f47daae694..b93072eddf 100644
--- a/framework/core/src/Formatter/Formatter.php
+++ b/framework/core/src/Formatter/Formatter.php
@@ -139,7 +139,7 @@ public function unparse($xml, $context = null)
             $xml = $callback($context, $xml);
         }
 
-        return Unparser::unparse($xml);
+        return $xml !== null ? Unparser::unparse($xml) : null;
     }
 
     /**