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', 'cs9sff18e9kbotq88nsa33ra10', '18.97.9.168', '1752891500', '1752891500', '/xtshop/product_info.php?info=p420_.html')

[XT SQL Error]