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', 'd81b2e6bmdg8ivj19mh9d8jvp0', '216.73.216.197', '1751518729', '1751518729', '/product_info.php?info=p15_25-balloons.html&XTCsid=ca28ab8f46bb6e791b42fe9b92719761')

[XT SQL Error]