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', '66ddca3962400b4685fd68134dbe6888', '216.73.216.190', '1776270940', '1776270940', '/shop/index.php?cat=c3_.html')

[XT SQL Error]