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', 'a6720e2b21fa6ea9074133d502a251ac', '216.73.216.219', '1772242236', '1772242236', '/shop/product_info.php?info=p112_.html')

[XT SQL Error]