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', '872o3qutjnfnontgjtfme61tp1', '216.73.216.9', '1758214128', '1758214128', '/index.php?XTCsid=fa57db38990172de3d9f1a0cbbc00d4e')

[XT SQL Error]