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', 'm21u0jukdnifguvri01q52an77', '216.73.216.121', '1761809743', '1761809743', '/popup_content.php?XTCsid=bc9e570ffcfa9dcf135106e019176796&coID=1')

[XT SQL Error]