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', 'nklhh6um4o5hluhdesil243lf3', '18.97.9.168', '1742456329', '1742456329', '/xtshop/index.php?cat=c21_.html')

[XT SQL Error]