Нулевая ссылка JSONObject и утечка активности

Я разрабатываю приложение для Android, подключенное к серверу, используя PHP на стороне сервера для хранения данных через MySQL. Итак, если я попытаюсь обобщить, ниже приведены ошибки в моем LogCat:

03-18 01:54:50.952    1930-2127/com.example.umitkaya.usermaintenanceactivity E/JSON Parser﹕ Error parsing data org.json.JSONException: End of input at character 1 of
--------- beginning of crash
03-18 01:54:50.977    1930-2127/com.example.umitkaya.usermaintenanceactivity E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #1
Process: com.example.umitkaya.usermaintenanceactivity, PID: 1930
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:300)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:818)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String org.json.JSONObject.toString()' on a null object reference
at com.example.umitkaya.usermaintenanceactivity.AllUserActivity$LoadAllUser.doInBackground(AllUserActivity.java:129)
at com.example.umitkaya.usermaintenanceactivity.AllUserActivity$LoadAllUser.doInBackground(AllUserActivity.java:104)
at android.os.AsyncTask$2.call(AsyncTask.java:288)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
03-18 01:54:54.127    1930-1930/com.example.umitkaya.usermaintenanceactivity E/WindowManager﹕ android.view.WindowLeaked: Activity com.example.umitkaya.usermaintenanceactivity.AllUserActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{97d499 V.E..... R......D 0,0-1026,348} that was originally added here
at android.view.ViewRootImpl.<init>(ViewRootImpl.java:363)
at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:261)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69)
at android.app.Dialog.show(Dialog.java:298)
at com.example.umitkaya.usermaintenanceactivity.AllUserActivity$LoadAllUser.onPreExecute(AllUserActivity.java:116)
at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:587)
at android.os.AsyncTask.execute(AsyncTask.java:535)
at com.example.umitkaya.usermaintenanceactivity.AllUserActivity.onCreate(AllUserActivity.java:59)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

И это мой исходный код:

public class AllUserActivity extends ListActivity{

// Progress Dialog
private ProgressDialog pDialog;

// Creating JSON Parser object
JSONParser jParser = new JSONParser();

ArrayList<HashMap<String, String>> userList;

// url to get all products list
private static String url_all_user = "http://10.0.2.2:8080/android_connect/get_all_users.php";

// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_USER = "user";
private static final String TAG_PID = "pid";
private static final String TAG_NAME = "name";

// products JSONArray
JSONArray user = null;

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

// Hashmap for ListView
userList = new ArrayList<HashMap<String, String>>();

// Loading products in Background Thread
new LoadAllUser().execute();

// Get listview
ListView lv = getListView();

// on seleting single product
// launching Edit Product Screen
lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {

@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// getting values from selected ListItem
String pid = ((TextView) view.findViewById(R.id.pid)).getText()
.toString();

// Starting new intent
Intent in = new Intent(getApplicationContext(),
EditUserActivity.class);
// sending pid to next activity
in.putExtra(TAG_PID, pid);

// starting new activity and expecting some response back
startActivityForResult(in, 100);
}
});
}
// Response from Edit Product Activity
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
// if result code 100
if (resultCode == 100) {
// if result code 100 is received
// means user edited/deleted product
// reload this screen again
Intent intent = getIntent();
finish();
startActivity(intent);
}
}

/**
* Background Async Task to Load all product by making HTTP Request
* */
class LoadAllUser extends AsyncTask<String, String, String> {

/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(AllUserActivity.this);
pDialog.setMessage("Loading users. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}

/**
* getting All products from url
* */
protected String doInBackground(String... args) {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
// getting JSON string from URL
JSONObject json = jParser.makeHttpRequest(url_all_user, "GET", params);

// Check your log cat for JSON reponse
Log.d("All User: ", json.toString());

try {
// Checking for SUCCESS TAG
int success = json.getInt(TAG_SUCCESS);

if (success == 1) {
// products found
// Getting Array of Products
user = json.getJSONArray(TAG_USER);

// looping through All Products
for (int i = 0; i < user.length(); i++) {
JSONObject c = user.getJSONObject(i);

// Storing each json item in variable
String id = c.getString(TAG_PID);
String name = c.getString(TAG_NAME);

// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();

// adding each child node to HashMap key => value
map.put(TAG_PID, id);
map.put(TAG_NAME, name);

// adding HashList to ArrayList
userList.add(map);
}
} else {
// no products found
// Launch Add New product Activity
Intent i = new Intent(getApplicationContext(),
NewUserActivity.class);
// Closing all previous activities
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(i);
}
} catch (JSONException e) {

e.printStackTrace();
}

return null;
}

/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
// dismiss the dialog after getting all products
pDialog.dismiss();
// updating UI from Background Thread
runOnUiThread(new Runnable() {
public void run() {
/**
* Updating parsed JSON data into ListView
* */
ListAdapter adapter = new SimpleAdapter(
AllUserActivity.this, userList,
R.layout.list_iteam, new String[] { TAG_PID,
TAG_NAME},
new int[] { R.id.pid, R.id.name });
// updating listview
setListAdapter(adapter);
}
});
}
}
}

Соединение со стороной сервера не имеет проблем. Проблема с моим кодом Android. Я ценю помощь.