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', 'vu9pug8b9la1hfeo815mc2j6o1', '54.196.107.247', '1495571230', '1495571230', '/product_info.php?info=p650_Charles-Dickens---der-Weihnachtsabend.html')

[XT SQL Error]