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', '4a18440b171fa5917ded4f7f89559987', '216.73.216.219', '1772242352', '1772242352', '/shop/product_info.php?info=p81_.html')

[XT SQL Error]