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', '90j0baft80bqo5g25larl44s65', '216.73.216.9', '1758061532', '1758061532', '/index.php?XTCsid=8ee99138ec7aa15aacd05f873fbff240')

[XT SQL Error]