iRule for HTTP 204 response with content-type

[root@ve1023:Active] config  b virtual bar list
virtual bar {
   snat automap
   pool foo
   destination 172.28.19.79:80
   ip protocol 6
   rules myrule
   profiles {
      http {}
      tcp {}
   }
}
[root@ve1023:Active] config  b rule myrule list
rule myrule {
   when HTTP_REQUEST {
   if {[string tolower [HTTP::uri]] starts_with "/static/img/click"} {
      HTTP::respond 204 noserver "Content-Type" "image/gif" "Connection" "Close"
   }
}
}

[root@ve1023:Active] config  curl -I http://172.28.19.79/static/img/click/test
HTTP/1.0 204 No Content
Content-Type: image/gif
Connection: close
Content-Length: 0