1366 - Incorrect integer value: '' for column 'customer_id' at row 1

insert into whos_online (customer_id, full_name, ip_address, time_last_click, last_page_url, time_entry, session_id, http_referer) values ('', '[TEXT_SEARCH_ENGINE_AGENT]', '54.234.228.78', '1544864064', '/popup_content.php?coID=1&KeepThis=true&TB_iframe=true&height=400&width=600', '1544864064', '', '---')

[XT SQL Error]