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', '1knnt9eh4rhkhfhpkqgn7bu6c6', '216.73.216.31', '1775048988', '1775048988', '/index.php?XTCsid=8c15d273183189e5e8d39cad65237995')

[XT SQL Error]