Another instance of this issue presents itself (fresh Zen Cart 1.5.5) when searching for null:
Code:
[01-Apr-2016 12:41:38 America/New_York] Request URI: /zc155/index.php?main_page=advanced_search_result&search_in_description=1&keyword=null, IP address: ::1
#1  trigger_error() called at [C:\xampp\htdocs\zc155\includes\classes\db\mysql\query_factory.php:167]
#2  queryFactory->show_error() called at [C:\xampp\htdocs\zc155\includes\classes\db\mysql\query_factory.php:139]
#3  queryFactory->set_error() called at [C:\xampp\htdocs\zc155\includes\classes\db\mysql\query_factory.php:266]
#4  queryFactory->Execute() called at [C:\xampp\htdocs\zc155\includes\classes\split_page_results.php:78]
#5  splitPageResults->__construct() called at [C:\xampp\htdocs\zc155\includes\modules\pages\advanced_search_result\header_php.php:462]
#6  require(C:\xampp\htdocs\zc155\includes\modules\pages\advanced_search_result\header_php.php) called at [C:\xampp\htdocs\zc155\index.php:36]


[01-Apr-2016 12:41:38 America/New_York] PHP Fatal error:  1064:You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 1 :: select count(distinct p.products_id) as total  FROM (products p              LEFT JOIN manufacturers m              USING(manufacturers_id), products_description pd, categories c, products_to_categories p2c )              LEFT JOIN meta_tags_products_description mtpd              ON mtpd.products_id= p2c.products_id              AND mtpd.language_id = 1 WHERE (p.products_status = 1                AND p.products_id = pd.products_id                AND pd.language_id = 1                AND p.products_id = p2c.products_id                AND p2c.categories_id = c.categories_id  ==> (as called by) C:\xampp\htdocs\zc155\includes\classes\split_page_results.php on line 78 <== in C:\xampp\htdocs\zc155\includes\classes\db\mysql\query_factory.php on line 167