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', 'smffkua7gffn5ck654e74hh455', '216.73.217.80', '1790176644', '1790176644', '/index.php?XTCsid=ca28ab8f46bb6e791b42fe9b92719761&language=en')

[XT SQL Error]