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', '327b168bbb94dcb537554810647e8b7f', '216.73.216.52', '1759574748', '1759574748', '/shop/index.php?cat=c22_.html')

[XT SQL Error]