assert shutter file exists

    def get_shutter(self, detector=6):

        """ get flat data """

        if self.custom_flat is None:

            return os.path.join(

        fp = os.path.join(

            self.path_aux,

            "C6.2_ref_mbi",

            "CSST_MSC_MS_SHUTTER_{:02d}_{:04d}.fits".format(

                detector, 1 if self.ref_version is None else self.ref_version

            )

        )

        if not os.path.exists(fp):

            raise FileNotFoundError(fp)

        else:

            return self.custom_flat.format("flat", detector)

            return fp

    def get_axeconf(self):

        return os.path.join(self.path_aux, "axeconf")  # "/home/csstpipeline/L1Pipeline/aux/axeconf"