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', '4k9o85q58s2u642hc0oge4q291', '216.73.216.180', '1766229755', '1766229755', '/popup_content.php?XTCsid=38717c4dd62e88001622b2c7b8b8372a&coID=1')

[XT SQL Error]