$ _SERVER ['HTTP_X_REQUESTED_WITH'] is always empty on nginx php5-fpm server

Question

$ _SERVER ['HTTP_X_REQUESTED_WITH'] is always empty on nginx php5-fpm server

I have installed a new webserver with nginx and php5-fpm on Debian. But for some reason $ _SERVER ['HTTP_X_REQUESTED_WITH'] remains empty even if the request is sent from jquery or javascript. I tried all different options but it is not empty.

This is my fastcgi_param file

fastcgi_param  QUERY_STRING       $query_string;
fastcgi_param  REQUEST_METHOD     $request_method;
fastcgi_param  CONTENT_TYPE       $content_type;
fastcgi_param  CONTENT_LENGTH     $content_length;

fastcgi_param  SCRIPT_FILENAME    $document_root$fastcgi_script_name;
fastcgi_param  SCRIPT_NAME        $fastcgi_script_name;
fastcgi_param  REQUEST_URI        $request_uri;
fastcgi_param  DOCUMENT_URI       $document_uri;
fastcgi_param  DOCUMENT_ROOT      $document_root;
fastcgi_param  SERVER_PROTOCOL    $server_protocol;

fastcgi_param  GATEWAY_INTERFACE  CGI/1.1;
fastcgi_param  SERVER_SOFTWARE    nginx/$nginx_version;

fastcgi_param  REMOTE_ADDR        $remote_addr;
fastcgi_param  REMOTE_PORT        $remote_port;
fastcgi_param  SERVER_ADDR        $server_addr;
fastcgi_param  SERVER_PORT        $server_port;
fastcgi_param  SERVER_NAME        $server_name;
fastcgi_param  HTTP_X_REQUESTED_WITH   $http_x_requested_with;

Here is my nginx.conf

user www-data;
worker_processes 4;
pid /var/run/nginx.pid;

events {
        worker_connections 768;
        # multi_accept on;
}

http {

        ##
        # Basic Settings
        ##

        sendfile on;
        tcp_nopush on;
        tcp_nodelay on;
        keepalive_timeout 65;
        types_hash_max_size 2048;
        # server_tokens off;

        # server_names_hash_bucket_size 64;
        # server_name_in_redirect off;

        include /etc/nginx/mime.types;
        include /etc/nginx/proxy_params;
        default_type application/octet-stream;
        #client_max_body_size 200M;
        ##
        # Logging Settings
        ##

        access_log /var/log/nginx/access.log;
        error_log /var/log/nginx/error.log;

        ##
        # Gzip Settings
        ##

        gzip on;
        gzip_disable "msie6";

        # gzip_vary on;
        # gzip_proxied any;
        # gzip_comp_level 6;
        # gzip_buffers 16 8k;
        # gzip_http_version 1.1;
        # gzip_types text/plain text/css application/json application/x-javascript text/xml application/xml application/xml+rss text/javascript;

        ##
        # nginx-naxsi config
        ##
        # Uncomment it if you installed nginx-naxsi
        ##

        #include /etc/nginx/naxsi_core.rules;

        ##
        # nginx-passenger config
        ##
        # Uncomment it if you installed nginx-passenger
        ##

        #passenger_root /usr;
        #passenger_ruby /usr/bin/ruby;

        ##
        # Virtual Host Configs
        ##

        include /etc/nginx/conf.d/*.conf;
        include /etc/nginx/sites-enabled/*;
}


#mail {
#       # See sample authentication script at:
#       # http://wiki.nginx.org/ImapAuthenticateWithApachePhpScript
#
#       # auth_http localhost/auth.php;
#       # pop3_capabilities "TOP" "USER";
#       # imap_capabilities "IMAP4rev1" "UIDPLUS";
#
#       server {
#               listen     localhost:110;
#               protocol   pop3;
#               proxy      on;
#       }
#
#       server {
#               listen     localhost:143;
#               protocol   imap;
#               proxy      on;
#       }
#}

And this is my site file

server {
        listen   80 default_server;

        root /path/public;
        index index.php index.html index.htm;

        server_name domain.name;

        access_log /path/logs/access.log;
        error_log  /path/logs/error.log error;

        set $skip_cache 0;

        if ($request_method = POST) {
                set $skip_cache 1;
        }
        if ($query_string != "") {
                set $skip_cache 1;
        }

        location / {

                try_files $uri $uri/ /index.php$is_args$args;
        }



        # pass the PHP s to FastCGI server listening on /var/run/php5-fpm.sock
        location ~ \.php$ {
                try_files $uri /index.php =404;
                fastcgi_pass unix:/var/run/php5-fpm.sock;
                fastcgi_index index.php;
                fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
                include fastcgi_params;
                fastcgi_cache_bypass $skip_cache;
                fastcgi_no_cache $skip_cache;

        }

        error_page 404 /index.php;

        # Deny .htaccess file access
        location ~ /\.ht {
                deny all;
        }
}