'parse_request' action hook generates "Nothing Found" error message

I want to instantiate a function based on a URL and I’ve used the method detailed in this blog:

https://willnorris.com/2009/06/wordpress-plugin-pet-peeve-2-direct-calls-to-plugin-files

add_action('parse_request', 'team_parse_request');

function team_parse_request($wp){
  if (array_key_exists('event', $wp->query_vars)){
    renderPost();
  }
}

This works.

I have a link on my page as follows:
https://threepwood/teamtest/index.php?event=22

If I click on the link, it takes the event ID and renders the required page correctly.

However, it generates an error message at the bottom of the page which says “Nothing Found”.