custer fixed error in user id with email

plugins/custer/queries.php

@@ -9,8 +9,11 @@ if (!defined('ABSPATH')) {
 }
 
 
-function get_queries($user_id, $if_empty) {
+function get_queries($user_id, $if_empty = '') {
 	$special_queries = Custer::QUERIES;
+	if (is_null($user_id)) {
+		return null;
+	}
 
 	$queries = array();
 	foreach($special_queries as $query) {
@@ -22,6 +25,9 @@ function get_queries($user_id, $if_empty) {
 
 
 function find_author_page_url($user_id) {
+	if (is_null($user_id)) {
+		return null;
+	}
 	return get_author_posts_url($user_id);
 }
 
@@ -33,6 +39,9 @@ function find_author_page_url($user_id) {
 *
 */
 function find_user_post_url($user_id) {
+	if (is_null($user_id)) {
+		return null;
+	}
 	$user_post_url = '';
 
 	$args = array(