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', '99f8f94f1da4daf5f5870f30c92a5dc5', '216.73.216.213', '1767383221', '1767383221', '/shop/product_info.php?info=p10_.html')

[XT SQL Error]