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', '3h9pme39k814nlktre5fgjhp87', '216.73.216.180', '1767014161', '1767014161', '/index.php?XTCsid=a7653c303bc951a885d15df88af8cab9')

[XT SQL Error]