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', '9tp3topq1qhbk156hdqthh2343', '216.73.216.87', '1765880026', '1765880026', '/product_info.php?XTCsid=3547ee950f9337e348e5e07def1466f0&info=p15_25-balloons.html&language=de')

[XT SQL Error]