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', 'cd8e6f8ri21nc8eqev57h04957', '18.97.14.83', '1765232723', '1765232723', '/xtshop/index.php?cat=c59_.html')

[XT SQL Error]