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', 'g9rua34ng3883lns3h66sd4cn0', '216.73.216.249', '1751516838', '1751516838', '/xtshop/product_info.php?info=p990_.html')

[XT SQL Error]