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', 'k778ar3ofko6ts799v3mcph6f4', '216.73.216.94', '1751955650', '1751955650', '/xtshop/popup_content.php?coID=1')

[XT SQL Error]