The following warning occurs when viewing a search page with no query.

Warning: strpos(): Empty needle in plugins/jetpack/modules/infinite-scroll/infinity.php on line 452

        if ( false !== strpos( $post->post_title, current( $search_terms ) ) ) {
            return true;
        }
        return false;

With an empty s query var, $search_terms is an array with one empty element.