Add type annotation

lib/SimpleSAML/Error/UnserializableException.php

@@ -40,6 +40,8 @@ class UnserializableException extends Exception
 
         $this->class = get_class($original);
         $msg = $original->getMessage();
+
+        /** @var string|int $code */
         $code = $original->getCode();
 
         if (!is_int($code)) {