WP: Do not allow a blank search

gistfile1

<?php
function make_blank_search ($query){
    global $wp_query;
    if (isset($_GET['s']) && ($_GET['s']=='' || $_GET['s']==' ') ){
        wp_redirect( $_SERVER['SERVER_NAME'].'/map', 301 ); exit;
    }
    return $query;
}
add_action('pre_get_posts','make_blank_search');
?>