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', 'pg2lf6fahcgtev9pbs3hn9ppd3', '216.73.216.244', '1752216987', '1752216987', '/index.php?XTCsid=1d1c6e66d9b87b73e0af7ebc046a2669')

[XT SQL Error]