VE uses HtmlOutputRendererHelper internally to fetch the HTML for editing. For some pages, the ParserOutput returned by HtmlOutputRendererHelper::getHtml() returns null from ParserOutput::getLanguage(), triggering a warning.
In the last hour, 344 such warnings were logged, see https://logstash.wikimedia.org/goto/c64f88bee45085d45249087b13b69087.
Some requests that have triggered the warning:
- https://fi.wikipedia.org/w/api.php?action=visualeditor&editintro=&format=json&formatversion=2&paction=parse&page=Hiroshiman_ja_Nagasakin_pommitukset&preload=&preloadparams=&uselang=fi
- https://vi.wikipedia.org/w/api.php?action=visualeditor&editintro=&format=json&formatversion=2&paction=parse&page=Th%C3%A0nh_vi%C3%AAn%3AJ2team&preload=&preloadparams=&uselang=vi
- https://ja.m.wikipedia.org//w/api.php?action=visualeditor&editintro=&format=json&formatversion=2&paction=parse&page=%E5%8C%97%E6%B5%B7%E9%81%93%E9%81%93836%E5%8F%B7%E5%B3%B6%E7%89%A7%E7%BE%8E%E5%88%A9%E6%B2%B3%E7%B7%9A&preload=&preloadparams=&uselang=ja
