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', '4d9nhrcop4pha125opv0n69m87', '216.73.216.87', '1765723541', '1765723541', '/index.php?XTCsid=4a177549c6a71de0023f5e2b49c3e919')

[XT SQL Error]