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', 'u0fl44mi0pb3fjbu6kpn1m2mg6', '216.73.216.36', '1773842631', '1773842631', '/xtshop/index.php?cat=c5_.html')

[XT SQL Error]