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', 'n21i16fqup550c686q39u6ijn1', '216.73.216.180', '1766418323', '1766418323', '/index.php?XTCsid=c63b24e231384cad64f954428cedcfc2&cat=c4_Beer-Mugs.html')

[XT SQL Error]