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', 'u9jdlsuecfe43ucsct8c1k9p63', '23.20.15.141', '1493373691', '1493373691', '/')

[XT SQL Error]