Here is something else we should do: remove the default value of None to fileinfo in this function. Furthermore, have you checked that [the call to this function](https://github.com/theupdateframework/tuf/blob/6c2251c0bd1eb6187ca89c3750b50cb6efc9a11f/tuf/client/updater.py#L751) does not pass a fileinfo that is None?