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', '66b043d73109930cc2090deb1b170477', '216.73.217.75', '1789292222', '1789292222', '/shop/index.php?cat=c28_.html')

[XT SQL Error]