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', 'cdmrjhqte5pepri4bsl0pkg6g4', '216.73.216.9', '1758223407', '1758223407', '/index.php?XTCsid=1455d70b156c4853db961f68b595bbe7&language=de')

[XT SQL Error]