How to use the stingray.gti.cross_two_gtis function in stingray

lc2 = get_lightcurve_any_dataset(src_destination2, bck_destination2, gti_destination2, filters2, dt2)
        if not lc2:
            return common_error("Cant create lightcurve 2")

        # Prepares GTI2 if passed
        gti2 = load_gti_from_destination (gti_destination2)
        if not gti2:
            logging.debug("External GTIs 2 not loaded using defaults")
            gti2 = lc2.gti

        # Join gtis in one gti
        gti = None
        gti1_valid = gti1 is not None and len(gti1) > 0
        gti2_valid = gti2 is not None and len(gti2) > 0
        if gti1_valid and gti2_valid:
            gti = cross_two_gtis(gti1, gti2)
            logging.debug("GTIS crossed")
        elif gti1_valid and not gti2_valid:
            gti = gti1
            logging.debug("GTI 1 applied")
        elif not gti1_valid and gti2_valid:
            gti = gti2
            logging.debug("GTI 2 applied")

        # Creates the cross spectrum
        logging.debug("Create cross spectrum")

        if xds_type == 'Sng':
            xs = Crossspectrum(lc1=lc1, lc2=lc2, norm=norm, gti=gti)
        else:
            xs = AveragedCrossspectrum(lc1=lc1, lc2=lc2, segment_size=segm_size, norm=norm, gti=gti)