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', 'und815n23r49ket6os9a24dlh2', '216.73.216.244', '1752212093', '1752212093', '/shop_content.php?coID=7&XTCsid=679e5364f8ebcbd98062f6d07b727e6d')

[XT SQL Error]