Missing parameter in set_url_scheme_handler_gnome3?

I've been down a small rabbit hole, trying to figure out why some electron apps set themselves as the default text/html application. Based on what I've learned, it seems that they're using xdg-utils to set up custom URL protocols. Could it be that the issue is that on this line, it passes no 2nd param the first time, which defaults to text/html? See this too.