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', 'af9kd28pr1eu55jlvg31biup44', '216.73.216.82', '1752529642', '1752529642', '/index.php?cat=c4_Beer-Mugs.html&XTCsid=1ea6ae83a06864ae88742e98ecbda16e')

[XT SQL Error]