Ich bin immer HttpResponse aber Antwort.getEntity().getContent() zeigt NullPointerException

protected String doInBackground(String... urls) {
    String url = urls[0];
    String result = "";

    HttpResponse response = doResponse(url);

    if (response == null) {
        return result;
    } else {

        try {
            result = inputStreamToString(response.getEntity().getContent());

        } catch (IllegalStateException e) {
            Log.e(TAG, e.getLocalizedMessage(), e);

        } catch (IOException e) {
            Log.e(TAG, e.getLocalizedMessage(), e);
        }

    }

    return result;
}

Werde ich die post-Daten in die Datenbank ein, hier unten befestigte ich meine restlichen codes, so überprüfen Sie bitte, und klar, mein problem ist, bitte

private HttpResponse doResponse(String url) {

    HttpClient httpclient = new DefaultHttpClient(getHttpParams());

    HttpResponse response = null;

    try {
        switch (taskType) {

        case POST_TASK:
            HttpPost httppost = new HttpPost(url);
            //Add parameters
            httppost.setEntity(new UrlEncodedFormEntity(params));
            response = httpclient.execute(httppost);

            break;
        case GET_TASK:
            HttpGet httpget = new HttpGet(url);
            response = httpclient.execute(httpget);
            break;
        }
    } catch (Exception e) {

        Log.e(TAG, e.getLocalizedMessage(), e);

    }

    return response;
}

private String inputStreamToString(InputStream is) {

    String line = "";
    StringBuilder total = new StringBuilder();

    //Wrap a BufferedReader around the InputStream
    BufferedReader rd = new BufferedReader(new InputStreamReader(is));

    try {
        //Read response until the end
        while ((line = rd.readLine()) != null) {
            total.append(line);
        }
    } catch (IOException e) {
        Log.e(TAG, e.getLocalizedMessage(), e);
    }

    //Return full string
    return total.toString();
}

Ich bin immer NullPointerException auf folgende Zeile,

result = inputStreamToString(response.getEntity().getContent());.

Ich verstehe nicht, über Person und Inhalte.wer kann mir helfen??