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', '4enjo949qdl2o8ldssq4v489j3', '216.73.216.9', '1758163960', '1758163960', '/index.php?XTCsid=da7af52687b721e9bfcdf7197b12a16c')

[XT SQL Error]