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', 'c96g1h6lahnubgtu1aud75eob2', '216.73.216.94', '1751956573', '1751956573', '/xtshop/product_info.php?info=p994_.html')

[XT SQL Error]