SPDY: do not reject headers with empty value (ticket #396). A quote from SPDY draft 2 specification: "The length of each name and value must be greater than zero. A receiver of a zero-length name or value must send a RST_STREAM with code PROTOCOL error." But it appears that Chrome browser allows sending requests over SPDY/2 connection using JavaScript that contain headers with empty values. For better compatibility across SPDY clients and to be compliant with HTTP, such headers are no longer rejected. Also, it is worth noting that in SPDY draft 3 the statement has been changed so that it permits empty values for headers.

scgi_param  REQUEST_METHOD     $request_method;
scgi_param  REQUEST_URI        $request_uri;
scgi_param  QUERY_STRING       $query_string;
scgi_param  CONTENT_TYPE       $content_type;

scgi_param  DOCUMENT_URI       $document_uri;
scgi_param  DOCUMENT_ROOT      $document_root;
scgi_param  SCGI               1;
scgi_param  SERVER_PROTOCOL    $server_protocol;
scgi_param  HTTPS              $https if_not_empty;

scgi_param  REMOTE_ADDR        $remote_addr;
scgi_param  REMOTE_PORT        $remote_port;
scgi_param  SERVER_PORT        $server_port;
scgi_param  SERVER_NAME        $server_name;