functions.php

<?php

/**
 * Empty search redirect
 * https://www.billerickson.net/advanced-search-with-searchwp-and-facetwp/#empty-search
 */
function ea_empty_search_redirect( $query ) {
	if( $query->is_main_query() && ! is_admin() && $query->is_search() && empty( $query->query['s'] ) ) {
		wp_redirect( home_url( 'search' ) );
		exit;
	}
}
add_action( 'pre_get_posts', 'ea_empty_search_redirect' );