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', 'aff15e53e3dc09ff3611baf5f5318963', '216.73.217.108', '1776591942', '1776591942', '/shop/index.php?cat=c18_.html')

[XT SQL Error]