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', 'r6etc5peki28uaeb7n4fdhham7', '216.73.216.110', '1752972042', '1752972042', '/index.php?language=de&cat=c9_Tischdekoration.html&XTCsid=80c3e9fc87b53cb0d288d19ef4e9b63c')

[XT SQL Error]