im trying to make a register page on android using JSON. everytime i press register button on avd, i get an error "unfortunately database has stopped". i have a error on my logcat that i cannot understand. this my code. please someone help me.

this my register.java

import android.app.Activity;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONException;
import org.json.JSONObject;

import java.util.ArrayList;
import java.util.List;

public class Register extends Activity implements OnClickListener{

    private EditText user, pass;
    private Button  mRegister;

    // Progress Dialog
    private ProgressDialog pDialog;

    // JSON parser class
    JSONParser jsonParser = new JSONParser();

    //php register script

    //localhost :
    //testing on your device
    //put your local ip instead,  on windows, run CMD > ipconfig
    //or in mac's terminal type ifconfig and look for the ip under en0 or en1
    // private static final String REGISTER_URL = "http://xxx.xxx.x.x:1234/webservice/register.php";

    //testing on Emulator:
    private static final String REGISTER_URL = "http://10.0.2.2:1234/webservice/register.php";

    //testing from a real server:
    //private static final String REGISTER_URL = "http://www.mybringback.com/webservice/register.php";

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

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.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> {


        @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(
                        REGISTER_URL, "POST", params);

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

                // json success element
                success = json.getInt(TAG_SUCCESS);
                if (success == 1) {
                    Log.d("User Created!", json.toString());
                    finish();
                    return json.getString(TAG_MESSAGE);
                }else{
                    Log.d("Registering Failure!", json.getString(TAG_MESSAGE));
                    return json.getString(TAG_MESSAGE);

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

            return null;

        }

        protected void onPostExecute(String file_url) {
            // dismiss the dialog once product deleted
            pDialog.dismiss();
            if (file_url != null){
                Toast.makeText(Register.this, file_url, Toast.LENGTH_LONG).show();
            }

        }

    }


}

this is JSONparser.java

import android.util.Log;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.utils.URLEncodedUtils;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;

public class JSONParser {

    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";

    // constructor
    public JSONParser() {

    }


    public JSONObject getJSONFromUrl(final String url) {

        // Making HTTP request
        try {
            // Construct the client and the HTTP request.
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);

            // Execute the POST request and store the response locally.
            HttpResponse httpResponse = httpClient.execute(httpPost);
            // Extract data from the response.
            HttpEntity httpEntity = httpResponse.getEntity();
            // Open an inputStream with the data content.
            is = httpEntity.getContent();

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            // Create a BufferedReader to parse through the inputStream.
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            // Declare a string builder to help with the parsing.
            StringBuilder sb = new StringBuilder();
            // Declare a string to store the JSON object data in string form.
            String line = null;

            // Build the string until null.
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }

            // Close the input stream.
            is.close();
            // Convert the string builder data to an actual string.
            json = sb.toString();
        } catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " + e.toString());
        }

        // Try to parse the string to a JSON object
        try {
            jObj = new JSONObject(json);
        } catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " + e.toString());
        }

        // Return the JSON Object.
        return jObj;

    }


    // function get json from url
    // by making HTTP POST or GET mehtod
    public JSONObject makeHttpRequest(String url, String method,
                                      List<NameValuePair> params) {

        // Making HTTP request
        try {

            // check for request method
            if(method == "POST"){
                // request method is POST
                // defaultHttpClient
                DefaultHttpClient httpClient = new DefaultHttpClient();
                HttpPost httpPost = new HttpPost(url);
                httpPost.setEntity(new UrlEncodedFormEntity(params));

                HttpResponse httpResponse = httpClient.execute(httpPost);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();

            }else if(method == "GET"){
                // request method is GET
                DefaultHttpClient httpClient = new DefaultHttpClient();
                String paramString = URLEncodedUtils.format(params, "utf-8");
                url += "?" + paramString;
                HttpGet httpGet = new HttpGet(url);

                HttpResponse httpResponse = httpClient.execute(httpGet);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();
            }

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            json = sb.toString();
        } catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " + e.toString());
        }

        // try parse the string to a JSON object
        try {
            jObj = new JSONObject(json);
        } catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " + e.toString());
        }

        // return JSON String
        return jObj;

    }
}

and this my error

08-18 23:40:02.381    2000-2018/com.example.blackcustomzier.database E/Buffer Error? Error converting result java.lang.NullPointerException: lock == null
08-18 23:40:02.381    2000-2018/com.example.blackcustomzier.database E/JSON Parser? Error parsing data org.json.JSONException: End of input at character 0 of
08-18 23:40:02.391    2000-2018/com.example.blackcustomzier.database W/dalvikvm? threadid=15: thread exiting with uncaught exception (group=0xb0f37648)
08-18 23:40:02.391    2000-2018/com.example.blackcustomzier.database E/AndroidRuntime? FATAL EXCEPTION: AsyncTask #4
    java.lang.RuntimeException: An error occured while executing doInBackground()
            at android.os.AsyncTask$3.done(AsyncTask.java:299)
            at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
            at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
            at java.util.concurrent.FutureTask.run(FutureTask.java:239)
            at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
            at java.lang.Thread.run(Thread.java:841)
     Caused by: java.lang.NullPointerException
            at com.example.blackcustomzier.database.Register$CreateUser.doInBackground(Register.java:108)
            at com.example.blackcustomzier.database.Register$CreateUser.doInBackground(Register.java:74)
            at android.os.AsyncTask$2.call(AsyncTask.java:287)
            at java.util.concurrent.FutureTask.run(FutureTask.java:234)
            at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
            at java.lang.Thread.run(Thread.java:841)
08-18 23:40:02.501    2000-2000/com.example.blackcustomzier.database W/EGL_emulation? eglSurfaceAttrib not implemented
08-18 23:40:02.591    2000-2000/com.example.blackcustomzier.database W/EGL_emulation? eglSurfaceAttrib not implemented
08-18 23:40:02.981    2000-2000/com.example.blackcustomzier.database E/WindowManager? Activity com.example.blackcustomzier.database.Register has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{b1294c60 V.E..... R......D 0,0-1026,288} that was originally added here
    android.view.WindowLeaked: Activity com.example.blackcustomzier.database.Register has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{b1294c60 V.E..... R......D 0,0-1026,288} that was originally added here
            at android.view.ViewRootImpl.<init>(ViewRootImpl.java:345)
            at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:239)
            at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69)
            at android.app.Dialog.show(Dialog.java:281)
            at com.example.blackcustomzier.database.Register$CreateUser.onPreExecute(Register.java:85)
            at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)
            at android.os.AsyncTask.execute(AsyncTask.java:534)
            at com.example.blackcustomzier.database.Register.onClick(Register.java:70)
            at android.view.View.performClick(View.java:4240)
            at android.view.View.onKeyUp(View.java:7928)
            at android.widget.TextView.onKeyUp(TextView.java:5606)
            at android.view.KeyEvent.dispatch(KeyEvent.java:2647)
            at android.view.View.dispatchKeyEvent(View.java:7343)
            at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1393)
            at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1393)
            at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1393)
            at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1393)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchKeyEvent(PhoneWindow.java:1933)
            at com.android.internal.policy.impl.PhoneWindow.superDispatchKeyEvent(PhoneWindow.java:1408)
            at android.app.Activity.dispatchKeyEvent(Activity.java:2384)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:1860)
            at android.view.ViewRootImpl$ViewPostImeInputStage.processKeyEvent(ViewRootImpl.java:3791)
            at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3774)
            at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3379)
            at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3429)
            at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3398)
            at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3483)
            at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3406)
            at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3540)
            at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3379)
            at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3429)
            at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3398)
            at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3406)
            at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3379)
            at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3429)
            at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3398)
            at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3516)
            at android.view.ViewRootImpl$ImeInputStage.onFinishedInputEvent(ViewRootImpl.java:3666)
            at android.view.inputmethod.InputMethodManager$PendingEvent.run(InputMethodManager.java:1982)
            at android.view.inputmethod.InputMethodManager.invokeFinishedInputEventCallback(InputMethodManager.java:1698)
            at android.view.inputmethod.InputMethodManager.finishedInputEvent(InputMethodManager.java:1689)
            at android.view.inputmethod.InputMethodManager$ImeInputEventSender.onInputEventFinished(InputMethodManager.java:1959)
            at android.view.InputEventSender.dispatchInputEventFinished(InputEventSender.java:141)
            at android.os.MessageQueue.nativePollOnce(Native Method)
            at android.os.MessageQueue.next(MessageQueue.java:132)
            at android.os.Looper.loop(Looper.java:124)
            at android.app.ActivityThread.main(ActivityThread.java:5103)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCal

please help me to solve this thx