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', 'igokghfrj6j7t1mdrbvkoq2rn1', '216.73.216.165', '1752308415', '1752308415', '/product_info.php?language=de&info=p15_25-balloons.html&XTCsid=3547ee950f9337e348e5e07def1466f0')

[XT SQL Error]