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', '9fbl42k3en87auu6b2qh7ts6m2', '216.73.217.35', '1780545319', '1780545319', '/xtshop/index.php?cat=c17_.html')

[XT SQL Error]