Posting facebook data in my wampserver for Android

I created a database using wampserver in order to post facebook data(name,user id etc).

I have the LoginFragment class:

    public class LoginFragment extends Fragment  {

    private TextView mTextDetails;
    private CallbackManager mCallbackManager;
    private AccessTokenTracker mTokenTracker;
    private ProfileTracker mProfileTracker;
    private static final String TAG = "LoginFragment";
    String profile_name,profile_id;

    private FacebookCallback<LoginResult> mFacebookCallback = new FacebookCallback<LoginResult>() {
        @Override
        public void onSuccess(LoginResult loginResult) {
            Log.d(TAG, "onSuccess");
            AccessToken accessToken = loginResult.getAccessToken();
            Profile profile = Profile.getCurrentProfile();
            if (profile == null)
                Log.d(TAG,"Profile is null");
            mTextDetails.setText(constructWelcomeMessage(profile));

            profile_name = profile.getName();
            profile_id = profile.getId();

            Intent intent = new Intent(getActivity(), MainActivity.class);
            startActivity(intent);
        }


        @Override
        public void onCancel() {
            Log.d(TAG, "onCancel");
        }

        @Override
        public void onError(FacebookException e) {
            Log.d(TAG, "onError " + e);
        }
    };


    public LoginFragment() {
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mCallbackManager = CallbackManager.Factory.create();
        setupTokenTracker();
        setupProfileTracker();

        mTokenTracker.startTracking();
        mProfileTracker.startTracking();
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        return inflater.inflate(R.layout.login_button, container, false);
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        setupTextDetails(view);
        setupLoginButton(view);

    }

    @Override
    public void onResume() {
        super.onResume();
        Profile profile = Profile.getCurrentProfile();
        mTextDetails.setText(constructWelcomeMessage(profile));
    }

    @Override
    public void onStop() {
        super.onStop();
        mTokenTracker.stopTracking();
        mProfileTracker.stopTracking();
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        mCallbackManager.onActivityResult(requestCode, resultCode, data);
    }

    private void setupTextDetails(View view) {
        mTextDetails = (TextView) view.findViewById(R.id.text_details);
    }

    private void setupTokenTracker() {
        mTokenTracker = new AccessTokenTracker() {
            @Override
            protected void onCurrentAccessTokenChanged(AccessToken oldAccessToken, AccessToken currentAccessToken) {
                Log.d(TAG, "" + currentAccessToken);
            }
        };
    }

    private void setupProfileTracker() {
        mProfileTracker = new ProfileTracker() {
            @Override
            protected void onCurrentProfileChanged(Profile oldProfile, Profile currentProfile) {
                Log.d(TAG, "" + currentProfile);
                mTextDetails.setText(constructWelcomeMessage(currentProfile));
            }
        };
    }

    private void setupLoginButton(View view) {
        LoginButton mButtonLogin = (LoginButton) view.findViewById(R.id.login_button);
        mButtonLogin.setFragment(this);
//        if (Build.VERSION.SDK_INT >= 16)
//            mButtonLogin.setBackground(null);
//        else
//            mButtonLogin.setBackgroundDrawable(null);
        mButtonLogin.setCompoundDrawables(null, null, null, null);
        mButtonLogin.setReadPermissions("public_profile");
        mButtonLogin.registerCallback(mCallbackManager, mFacebookCallback);
    }

    private String constructWelcomeMessage(Profile profile) {
        StringBuffer stringBuffer = new StringBuffer();
        if (profile != null) {
            stringBuffer.append("Welcome " + profile.getName());
        }
        return stringBuffer.toString();
    }

}

Next I have the BackgroundTask class which makes HTTP connection to my database:

    public class BackgroundTask extends AsyncTask<String,Void,String>{
    Context ctx;
    BackgroundTask(Context ctx)
    {

        this.ctx=ctx;
    }

    @Override

    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected String doInBackground(String... params) {
        String createevent_url="10.0.2.2/webapp/createvent.php";

        String method = params[0];
        if (method.equals("profile")) {
            String profile_name=params[1];
            String profile_id =params[2];
            try {
                URL url = new URL(createevent_url);
                HttpURLConnection httpURLConnection = (HttpURLConnection)url.openConnection();
                httpURLConnection.setRequestMethod("POST");
                httpURLConnection.setDoOutput(true);
                OutputStream OS=httpURLConnection.getOutputStream();
                BufferedWriter bufferedWriter= new BufferedWriter(new OutputStreamWriter(OS,"UTF-8"));
                String data = URLEncoder.encode("profile_name","UTF-8")+"="+URLEncoder.encode(profile_name,"UTF-8")+"&"+
                        URLEncoder.encode("profile_id","UTF-8")+"="+URLEncoder.encode(profile_id,"UTF-8");

                bufferedWriter.write(data);
                bufferedWriter.flush();
                bufferedWriter.close();
                OS.close();

                InputStream IS=httpURLConnection.getInputStream();
                IS.close();

                return  "Profile success..";
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

        }

        return null;
    }

    @Override
    protected void onProgressUpdate(Void... values) {
        super.onProgressUpdate(values);
    }

    @Override
    protected void onPostExecute(String result) {
        Toast.makeText(ctx,result,Toast.LENGTH_LONG).show();
    }
}

And I have the MainActivity class where an object from BackgroundTask class is created and then I execute it.

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

private ListAdapter listAdapter;
String profile_name,profile_id;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
            this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
    drawer.setDrawerListener(toggle);
    toggle.syncState();

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);

    Profile profile = Profile.getCurrentProfile();
    profile_name = profile.getName();
    profile_id = profile.getId();
    String method = "profile";
    BackgroundTask backgroundTask = new BackgroundTask(this);
    backgroundTask.execute(method,profile_name,profile_id);
    finish();

    // Add sample data to event list.
    ListView listView = (ListView) findViewById(R.id.listView);
    listAdapter = TestData.getEventListAdapter(this);
    listView.setAdapter(listAdapter);
    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            Intent intent = new Intent(MainActivity.this, EventDetails.class);
            startActivity(intent);
        }
    });
}

When I run it I got RunTimeException and a NullPointerException. The NullPointerException happens inside LoginFragment class in the Facebook callback method where I call profile.getName().

It says that profile is null.

Why does this happen and how can I resolve it?