JSONStringer giving null object in Android 2.1 (update)

I am making post call to a web service by sending object in JSON format. I am using GSON to convert my object to JSON and JSONStringer to create key-value pair to send to server in a post call.

    JSONStringer billString = new JSONStri开发者_开发知识库nger().object()
                .key("details").value(new JSONObject(json));
   CustomHttpRequest request = new CustomHttpRequest(WebserviceBaseAddress);
        request.AddHeader("Accept", "application/json");
        request.AddHeader("Content-type", "application/json");
        request.AddParam("entity", billString.toString());
        request.GetRequest(RequestMethod.POST);

This line of code works fine in Android 2.2, but 2.1, billString is null. That is why I am getting null exception for (request.AddParam("entity", billString.toString());) Can anybody tell me what is the problem here? Or is there any way to make key-value pair to make post call in GSON, so that JSONStringer can be removed?

Thanks Ashwani

---

Change

JSONStringer billString = new JSONStringer().object()
                .key("details").value(new JSONObject(json));

to

String billString = new JSONStringer().object()
                .key("details").value(new JSONObject(json)).endObject().toString();

The object syntax needs to be balanced -- there is a beginning and an ending.