def load_session_from_file(self, username: str, filename: Optional[str] = None) -> None:
        """Internally stores :class:`requests.Session` object loaded from file.

        If filename is None, the file with the default session path is loaded.

        :raises FileNotFoundError: If the file does not exist.
        """
        if filename is None:
            filename = get_default_session_filename(username)
        with open(filename, 'rb') as sessionfile:
            self.context.load_session_from_file(username, sessionfile)
            self.context.log("Loaded session from %s." % filename)