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', 'rn336q23kbaa2pqe5mn367qca2', '216.73.216.209', '1766852727', '1766852727', '/xtshop/product_info.php?info=p920_.html')

[XT SQL Error]