Redirect on lack of query_var

function redirect_to_homepage($query) {
    if($query->is_page('manage') || $query->is_page('settings')) {
        if((!array_key_exists('username', $query->query_vars) || (array_key_exists('username', $query->query_vars) && trim($query->query_vars['username']) == '' ))) {
            wp_redirect(get_bloginfo('url'));
            exit;
        }
    }
}
add_action('parse_query', 'redirect_to_homepage');