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', 'm8t2mt0kqcj2fh7utkmuams7u0', '216.73.217.25', '1781319108', '1781319108', '/index.php?XTCsid=979063553d403df75eb8c32c59325da8&language=de')

[XT SQL Error]