Mysterious 404 /undefined

Request 17: http://www.paulmassendari.com/undefined
URL: http://www.paulmassendari.com/undefined
Host: www.paulmassendari.com
IP: 104.27.147.26
Error/Status Code: 404
Initiated By: http://www.paulmassendari.com/ line 1
Client Port: 2290
Request Start: 1.536 s
Time to First Byte: 1858 ms
Content Download: 15 ms
Bytes In (downloaded): 3.9 KB
Bytes Out (uploaded): 0.6 KB
Request Headers:

GET /undefined HTTP/1.1
Host: www.paulmassendari.com
Connection: keep-alive
Accept: image/webp,image/*,*/*;q=0.8
User-Agent: Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.112 Safari/537.36 PTST/201
Referer: http://www.paulmassendari.com/
Accept-Encoding: gzip, deflate, sdch
Accept-Language: fr-FR,fr;q=0.8,en-US;q=0.6,en;q=0.4
Cookie: __cfduid=da550b45a3f7f4129f7ecc5ae63f4517f1463834633; 300gpBAK=R4178755467; 300gp=R393486697; grav-site-6adfb31=e0ca64f91b8010587add0cfd79c5e252; grav-site-6adfb31=e0ca64f91b8010587add0cfd79c5e252; _ga=GA1.2.33581958.1463834674; _gat=1
Response Headers:

HTTP/1.1 404 Not Found
Date: Sat, 21 May 2016 12:43:57 GMT
Content-Type: text/html;charset=UTF-8
Transfer-Encoding: chunked
Connection: keep-alive
Set-Cookie: 300gp=R393486697; path=/; expires=Sat, 21-May-2016 13:45:11 GMT
X-Powered-By: PHP/5.6.21
Pragma: no-cache
Set-Cookie: grav-site-6adfb31=e0ca64f91b8010587add0cfd79c5e252; expires=Sat, 21-May-2016 13:13:55 GMT; Max-Age=1800; path=/; domain=www.paulmassendari.com; httponly
Cache-Control: max-age=604800
Expires: Sat, 28 May 2016 12:43:57 GMT
Vary: Accept-Encoding
Server: cloudflare-nginx
CF-RAY: 2a681de61e431037-CDG
Content-Encoding: gzip