An index file is part of your website… creating a Virtual Server makes it so that you can upload a website.
But – by default – it doesn’t upload one for you, as it doesn’t know what you want there
One way to have a default site put in place would be to create it in /etc/skel/public_html.
The contents of /etc/skel are used for new sites. If you create a /etc/skel/public_html/index.html file, it would be copied to every new Virtual Server created.