Problem with application/octet-stream content-type

Server NGINX
#1

How to configure that?

the files xxx-yyy-ddd-hhh and xxx-yyy-ddd-hhh.html have the same html
code
in it.

Typing example.com/xxx-yyy-ddd-hhh.html in the browser is OK.

Typing example.com/xxx-yyy-ddd-hhh in the browser get the wronge
content-type application/octet-stream.
A text/html content-type is need.

Posted at Nginx Forum:
http://forum.nginx.org/read.php?2,248575,248575#msg-248575

#2

Nginx binds file extensions with file types:
http://nginx.org/en/docs/http/ngx_http_core_module.html#types
An examples there links to
http://nginx.org/en/docs/http/ngx_http_core_module.html#default_type

B. R.