Dúvida no Ex. 1 da Aula 2 - Fazendo o envio dos dados de forma assíncrona

Oi Pessoal,

Meu código está dando um erro quando tentar fazer a conexão com o servidor que eu ainda não consegui identificar.

A classe WebClient está assim:

public class WebClient {

    private URL url;

    public WebClient(String url) throws MalformedURLException{

            this.url = new URL(url);

    }

    @SuppressWarnings("resource")
    public String post (String json) throws InterruptedException, IOException{

            String resposta = null;
            HttpURLConnection connection;

            connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("POST");
            connection.setRequestProperty("Content-type", "application/json");
            connection.setRequestProperty("Accept", "application/json");

            connection.setDoOutput(true);

            PrintStream saida = new PrintStream(connection.getOutputStream());

            saida.println(json);
            connection.connect();

            resposta = new Scanner(connection.getInputStream()).next();

            return resposta;

    }
}


O método doInBackground:

protected String doInBackground(Object... params) {

        DBHelper dbHelper = new DBHelper(this.ctx);
        List<Aluno> alunos = dbHelper.getListaAlunos();
        String json = new AlunoConverter().toJSON(alunos);


            try {
                WebClient cliente = new WebClient("http://www.caelum.com.br/mobile");
                String resp;
                resp = cliente.post(json);
                return resp;

            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }


        return null;
    }

E o LogCat:

10-08 13:32:26.138: E/AndroidRuntime(1260): FATAL EXCEPTION: AsyncTask #1
10-08 13:32:26.138: E/AndroidRuntime(1260): Process: br.com.lacouth.cadastro, PID: 1260
10-08 13:32:26.138: E/AndroidRuntime(1260): java.lang.RuntimeException: An error occured while executing doInBackground()
10-08 13:32:26.138: E/AndroidRuntime(1260):     at android.os.AsyncTask$3.done(AsyncTask.java:300)
10-08 13:32:26.138: E/AndroidRuntime(1260):     at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
10-08 13:32:26.138: E/AndroidRuntime(1260):     at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
10-08 13:32:26.138: E/AndroidRuntime(1260):     at java.util.concurrent.FutureTask.run(FutureTask.java:242)
10-08 13:32:26.138: E/AndroidRuntime(1260):     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
10-08 13:32:26.138: E/AndroidRuntime(1260):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
10-08 13:32:26.138: E/AndroidRuntime(1260):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
10-08 13:32:26.138: E/AndroidRuntime(1260):     at java.lang.Thread.run(Thread.java:841)
10-08 13:32:26.138: E/AndroidRuntime(1260): Caused by: java.util.NoSuchElementException
10-08 13:32:26.138: E/AndroidRuntime(1260):     at java.util.Scanner.next(Scanner.java:961)
10-08 13:32:26.138: E/AndroidRuntime(1260):     at java.util.Scanner.next(Scanner.java:934)
10-08 13:32:26.138: E/AndroidRuntime(1260):     at br.com.lacouth.suporte.WebClient.post(WebClient.java:46)
10-08 13:32:26.138: E/AndroidRuntime(1260):     at br.com.lacouh.task.EnvioDeAlunos.doInBackground(EnvioDeAlunos.java:39)
10-08 13:32:26.138: E/AndroidRuntime(1260):     at br.com.lacouh.task.EnvioDeAlunos.doInBackground(EnvioDeAlunos.java:1)
10-08 13:32:26.138: E/AndroidRuntime(1260):     at android.os.AsyncTask$2.call(AsyncTask.java:288)
10-08 13:32:26.138: E/AndroidRuntime(1260):     at java.util.concurrent.FutureTask.run(FutureTask.java:237)
10-08 13:32:26.138: E/AndroidRuntime(1260):     ... 4 more