I'm new in gwt and new in using firebug.I have valid json result from tesdb3.php

{"item": [{"kode":"002","nama":"bambang gentolet"},
          {"kode":"012","nama":"Algiz"}]}

I add the xml with

inherits name='com.google.gwt.json.JSON'/
inherits name="com.google.gwt.http.HTTP" /

then i try to show it in the gwt with this code.

public class Tesdb3 implements EntryPoint { 

String url= "http://localhost/phpmyadmin/tesdb3/datauser.php";

public void LoadData() throws RequestException{             

    RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, URL.encode(url));

    builder.sendRequest(null, new RequestCallback(){
        @Override
        public void onError(Request request, Throwable exception) {
            Window.alert("error " + exception);
        }
        public void onResponseReceived(Request request,
                Response response) {
              if (200 == response.getStatusCode()) {
                  Window.alert("ok -" + response.getText() + "-" + response.getStatusCode());
              } else {
                  Window.alert("error2 -" + response.getText()+ response.getStatusText() + "-" + response.getStatusCode());
              }         
        }
    });
}

public void onModuleLoad() {        
    try {
        LoadData();
    } catch (RequestException e) {
        e.printStackTrace();
    }       
}

}
I run it in development mode. not hosted mode.
My code didn't show any error. But the result in window alert is "error2 --OK-0".

result Net from firebug is 7 request:
get Tesdb3.html?gwt.codeserv = 200ok
get Tesdb3.css = 200ok
get tesdb3.nocache.js = 200ok
get hosted.html?tesdb3 = aborted
get standard.css = 304 not modified
get hosted.html?tesdb3 = 403 not modified
get datauser.php = 200ok

my question is:

Why the response status code is 0, and the response status text is 'OK'? there was no eror in json or java code.

why response.getText is empty? Why i can't get any json result even a single character?