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', 'aog16d87ulvj9bigm2ti7r4qt1', '216.73.216.230', '1781162487', '1781162487', '/xtshop/index.php')

[XT SQL Error]