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', 'b2doivoqcj7qavm8cp4espjm55', '216.73.216.147', '1751757721', '1751757721', '/product_info.php?language=de&info=p8_100-Placemats.html&XTCsid=9265b55633a2cb4e8ed6db3536c73ca5')

[XT SQL Error]