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', 'qk2j51rslrki3l5bie570oqrj3', '107.22.127.78', '1493220794', '1493220794', '/product_info.php?info=p139_Held.html')

[XT SQL Error]