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', '91ju044sj5op25p74eh9fqpcs2', '3.80.128.196', '1555648553', '1555648553', '/shop/index.php?cat=c77_Watkescher.html')

[XT SQL Error]