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', 'k1kav28n688pod6hntc5et1m36', '216.73.216.49', '1752611932', '1752611932', '/xtshop/product_info.php?info=p394_.html')

[XT SQL Error]