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', '6mnkqqdc9asrc6mv6hnj707ds0', '216.73.216.230', '1781162357', '1781162357', '/xtshop/index.php')

[XT SQL Error]