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', 'prc3g8vcbc2r220t6jfvohbum2', '35.171.183.163', '1563243155', '1563243155', '/shop/advanced_search.php?XTCsid=prc3g8vcbc2r220t6jfvohbum2')

[XT SQL Error]