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', '93b62pqorsnhh9dtsfq1vg0cr1', '216.73.216.63', '1773907171', '1773907171', '/index.php?XTCsid=6bb5e4d6110a5fe0c19bd41c6b302c38&cat=c5_Crockery.html&language=de')

[XT SQL Error]