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', '0nsm8s8hgiql5gnf8vv48raot1', '216.73.216.7', '1758237224', '1758237224', '/index.php?XTCsid=a0c8d0b3d08cb472c84559a313755d47&language=de')

[XT SQL Error]