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', '9e4618c321230de552c058f68a792031', '216.73.216.38', '1776433301', '1776433301', '/shop/product_info.php?info=p149_.html')

[XT SQL Error]