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', '5lncm1qmbcbblove9kpgra7a40', '216.73.216.58', '1771713436', '1771713436', '/index.php?XTCsid=744c226086359bc1d698caea9179572f')

[XT SQL Error]