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', 'ohnkj2ka4qsh3t6bkn7q3m4473', '216.73.216.209', '1767336318', '1767336318', '/xtshop/index.php?cat=c27_.html')

[XT SQL Error]