1366 - Incorrect integer value: '' for column 'customer_id' at row 1

insert into whos_online (customer_id, full_name, session_id, ip_address, time_entry, time_last_click, last_page_url) values ('', 'Guest', 't6cfau631985ikp9t6je7l1pq4', '216.73.216.33', '1771221740', '1771221740', '/xtshop/product_info.php?info=p557_.html')

[XT SQL Error]