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', 'hubf8r5572v0o41b4lktrd1dm5', '216.73.216.113', '1752884248', '1752884248', '/product_info.php?language=de&info=p21_Paper-tablecloth-10-meters.html&XTCsid=4cf293bb00c65c9a710c393a6b5a73c4')

[XT SQL Error]