bug: SitemapRequestList.persistState() throws when sitemap loading has finished

bug: SitemapRequestList.persistState() throws when sitemap loading has finished: a task in MiMo-V2.6-RL-harbor-code: MiMo-V2.6-RL Code (Harbor) (Harbor dataset). This is because after parsing the sitemaps fully, the SitemapRequestList closes the internal stream with .push(null)…