Asynctask中的错误：执行doInBackground（）

Question

我正在尝试使用相同的方法进行登录和注册活动登录系统工作正常但是在注册系统中它给出了错误，我无法找到错误，就像在logcat中我的代码是

public class Register extends Activity implements OnClickListener {

private Button btnLinkToLogin;
private EditText user, pass;
private Button mRegister;
private ProgressDialog pDialog;

JSONParser jsonParser = new JSONParser();

private static final String LOGIN_URL = "http://http://portfolio.webuda.com/register.php";

private static final String TAG_SUCCESS = "success";
private static final String TAG_MESSAGE = "message";


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_register);

    user = (EditText) findViewById(R.id.username);
    pass = (EditText) findViewById(R.id.password);

    mRegister = (Button) findViewById(R.id.register);
    mRegister.setOnClickListener(this);
}


@Override
public void onClick(View v) {
    // TODO Auto-generated method stub

    new CreateUser().execute();
}

class CreateUser extends AsyncTask<String, String, String> {

    /**
     * Before starting background thread Show Progress Dialog
     */
    boolean failure = false;

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = new ProgressDialog(Register.this);
        pDialog.setMessage("Creating User...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(true);
        pDialog.show();
    }

    @Override
    protected String doInBackground(String... args) {
        // TODO Auto-generated method stub
        // Check for success tag
        int success;
        String username = user.getText().toString();
        String password = pass.getText().toString();
        try {
            // Building Parameters
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("username", username));
            params.add(new BasicNameValuePair("password", password));

            Log.d("request!", "starting");

            //Posting user data to script
            JSONObject json = jsonParser.makeHttpRequest(
                    LOGIN_URL, "POST", params);

            // full json response
            Log.d("Login attempt", json.toString());

            // json success element
            success = json.getInt(TAG_SUCCESS);
            if (success == 1) {
                Log.d("User Created!", json.toString());
                Intent ii = new Intent(Register.this,HomeActivity.class);
                finish();
                startActivity(ii);
                return json.getString(TAG_MESSAGE);
            } else {
                Log.d("Login Failure!", json.getString(TAG_MESSAGE));
                return json.getString(TAG_MESSAGE);

            }
        } catch (JSONException e) {
            e.printStackTrace();
        }

        return null;

    }

    protected void onPostExecute(String file_url) {

        pDialog.dismiss();
        if (file_url != null) {
            Toast.makeText(Register.this, file_url, Toast.LENGTH_LONG).show();
        }
    }
}
}