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', 'lcn1s93irpl4596geuj0ekqs37', '216.73.216.9', '1758139771', '1758139771', '/index.php?XTCsid=a0c8d0b3d08cb472c84559a313755d47&language=en')

[XT SQL Error]