Proper default null value in reset()

src/codegen.inc.php

@@ -369,7 +369,7 @@ function var_reset($name, \mtgType $type, $default = null)
         }
       }
       else if($default === null)
-        $str .= "$name = default; ";
+        $str .= "$name = null; ";
       else
         throw new Exception("Bad default value for struct: " . var_export($default, true));
     }