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', 'q4rnfl0dvqv7tng6ddj4889r70', '216.73.216.212', '1788712543', '1788712543', '/xtshop/index.php?cat=c90_.html')

[XT SQL Error]