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', '7lvgtn1nk1p7jckla9n8gq7ag0', '216.73.216.9', '1757785269', '1757785269', '/product_info.php?XTCsid=c3021bf24ae7ff6e625e518984d013cd&info=p8_100-Placemats.html&language=de')

[XT SQL Error]