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', '25b8dbc84453502b1ab7671edf3e8eee', '216.73.216.52', '1759534760', '1759534760', '/shop/index.php?cat=c13_.html')

[XT SQL Error]