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', 'd87bdff2e90d7befebbfffdda8f0d4a5', '216.73.216.195', '1781349321', '1781349321', '/shop/login.php')

[XT SQL Error]