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', 'd1a72621aaaa41a50dda7caafd5cb0b0', '216.73.216.148', '1774713454', '1774713454', '/shop/index.php')

[XT SQL Error]