Ribbit: Null pointer at User Adapter

ParseUser user = mUsers.get(position);
String email = "";

if (user != null)
    email = user.getEmail().toLowerCase();

if (email.equals("")) {
    holder.userImageView.setImageResource(R.drawable.avatar_empty);
}

public class MyActivity extends FragmentActivity implements ActionBar.TabListener {

    public static String TAG = MyActivity.class.getSimpleName();


    public static  final int TAKE_PHOTO_REQUEST = 0;
    public static  final int TAKE_VIDEO_REQUEST = 1;
    public static  final int PICK_PHOTO_REQUEST = 2;
    public static  final int PICK_VIDEO_REQUEST = 3;

    public static final int MEDIA_TYPE_IMAGE = 4;
    public static final int MEDIA_TYPE_VIDEO = 5;

    public static final int FILE_SIZE_LIMIT = 1024*1024*10; //5MB


    protected Uri mMediaUri;


    protected DialogInterface.OnClickListener mDialogListener =
            new DialogInterface.OnClickListener() {


                @Override
                public void onClick(DialogInterface dialogInterface, int i) {
                    switch (i) {
                        case 0: //Picture
                            Intent takePhotoIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
                            mMediaUri = getOutputMediaFileUri(MEDIA_TYPE_IMAGE);
                            if (mMediaUri == null){
                                //display error
                                Toast.makeText(MyActivity.this, R.string.error_external_storage, Toast.LENGTH_LONG).show();
                            }
                            else{
                            takePhotoIntent.putExtra(MediaStore.EXTRA_OUTPUT, mMediaUri);
                            startActivityForResult(takePhotoIntent, TAKE_PHOTO_REQUEST);
                            }
                            break;
                        case 1: //Video
                            Intent takeVideoIntent = new Intent(MediaStore.ACTION_VIDEO_CAPTURE);
                            mMediaUri = getOutputMediaFileUri(MEDIA_TYPE_VIDEO);

                            if (mMediaUri == null) {
                                //display error
                                Toast.makeText(MyActivity.this, R.string.error_external_storage, Toast.LENGTH_LONG).show();
                            }
                        else{

                                takeVideoIntent.putExtra(MediaStore.EXTRA_OUTPUT, mMediaUri);
                                takeVideoIntent.putExtra(MediaStore.EXTRA_DURATION_LIMIT, 10);
                                takeVideoIntent.putExtra(MediaStore.EXTRA_VIDEO_QUALITY, 0);
                                startActivityForResult(takeVideoIntent,TAKE_VIDEO_REQUEST);



                            }

                            break;
                        case 2: //Choose Pic

                            Intent choosePhotoIntent = new Intent(Intent.ACTION_GET_CONTENT);
                            choosePhotoIntent.setType("image/*");
                            startActivityForResult(choosePhotoIntent, PICK_PHOTO_REQUEST);
                            break;
                        case 3: //Choose Video
                            Intent chooseVideoIntent = new Intent(Intent.ACTION_GET_CONTENT);
                            chooseVideoIntent.setType("video/*");
                            Toast.makeText(MyActivity.this,getString(R.string.video_message), Toast.LENGTH_LONG).show();
                            startActivityForResult(chooseVideoIntent, PICK_VIDEO_REQUEST);
                            break;
                        }
                    }

                private Uri getOutputMediaFileUri(int mediaType) {
                    // To be safe, you should check that the SDCard is mounted
                    // using Environment.getExternalStorageState() before doing this.
                    if (isExternalStorageAvailable()) {
                        //Get Uri
                        //1. Get ex storage directory
                        String appName = MyActivity.this.getString(R.string.app_name);
                        File mediaStorageDir = new File(
                                Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES), appName);
                        //2. Create own subdirectory
                        if (!mediaStorageDir.exists()) {
                            if (!mediaStorageDir.mkdirs()) {
                                Log.e(TAG, "Failed to create directory");
                                return null;
                            }
                        }
                        //3.Create file name
                        //4.Create the file

                        File mediaFile;
                        Date now = new Date();
                        String timestamp = new SimpleDateFormat("yyyyMMdd_HHmmss", Locale.US).format(now);

                        String path = mediaStorageDir.getPath() + File.separator;
                        if (mediaType == MEDIA_TYPE_IMAGE) {
                            mediaFile = new File(path + "IMG_" + timestamp + ".jpeg");
                        } else if (mediaType == MEDIA_TYPE_VIDEO) {
                            mediaFile = new File(path + "VID_" + timestamp + ".mp4");
                        } else {
                            return null;
                        }
                        Log.d(TAG, "File" + Uri.fromFile(mediaFile));
                        //5. return file's Uri
                        return Uri.fromFile(mediaFile);
                    }
                        else {
                            return null;
                        }




                    }



                private boolean isExternalStorageAvailable() {
                    String state = Environment.getExternalStorageState();

                    if (state.equals(Environment.MEDIA_MOUNTED)){
                        return true;
                    }
                    else{
                        return false;
                    }
                }
            };









    /**
     * The {@link android.support.v4.view.PagerAdapter} that will provide
     * fragments for each of the sections. We use a
     * {@link FragmentPagerAdapter} derivative, which will keep every
     * loaded fragment in memory. If this becomes too memory intensive, it
     * may be best to switch to a
     * {@link android.support.v13.app.FragmentStatePagerAdapter}.
     */
    SectionsPagerAdapter mSectionsPagerAdapter;

    /**
     * The {@link ViewPager} that will host the section contents.
     */
    ViewPager mViewPager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
        setContentView(R.layout.activity_my);

        ParseAnalytics.trackAppOpened(getIntent());
        ButterKnife.inject(this);




        //ParseUser.logOut();
        ParseUser currentUser = ParseUser.getCurrentUser();

        if(currentUser==null){
            GoToLogin();
        }
        else{
            Log.i(TAG, currentUser.getUsername());
        }

        // Set up the action bar.
        final ActionBar actionBar = getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        // Create the adapter that will return a fragment for each of the three
        // primary sections of the activity.
        mSectionsPagerAdapter = new SectionsPagerAdapter(this,getSupportFragmentManager());

        // Set up the ViewPager with the sections adapter.
        mViewPager = (ViewPager) findViewById(R.id.pager);
        mViewPager.setAdapter(mSectionsPagerAdapter);

        // When swiping between different sections, select the corresponding
        // tab. We can also use ActionBar.Tab#select() to do this if we have
        // a reference to the Tab.
        mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
            @Override
            public void onPageSelected(int position) {
                actionBar.setSelectedNavigationItem(position);
            }
        });

        // For each of the sections in the app, add a tab to the action bar.
        for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
            // Create a tab with text corresponding to the page title defined by
            // the adapter. Also specify this Activity object, which implements
            // the TabListener interface, as the callback (listener) for when
            // this tab is selected.
            actionBar.addTab(
                    actionBar.newTab()
                            .setIcon(mSectionsPagerAdapter.getIcon(i))
                            .setTabListener(this));
        }
    }




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

        if (resultCode == RESULT_OK) {
            if (requestCode == PICK_PHOTO_REQUEST || requestCode == PICK_VIDEO_REQUEST) {
                if (data == null) {
                    Toast.makeText(this, getString(R.string.general_error), Toast.LENGTH_LONG).show();
                } else {
                    mMediaUri = data.getData();
                }
                Log.i(TAG, "Media URI: " + mMediaUri);
                if (requestCode == PICK_VIDEO_REQUEST) {
                    //make sure file less than 10MB
                    int fileSize = 0;
                    InputStream inputStream = null;
                    try {
                        inputStream = getContentResolver().openInputStream(mMediaUri);
                        fileSize = inputStream.available();
                    } catch (FileNotFoundException e) {
                        Toast.makeText(this, getString(R.string.filesize_error), Toast.LENGTH_LONG).show();
                        return;
                    } catch (IOException e) {
                        Toast.makeText(this, getString(R.string.filesize_error), Toast.LENGTH_LONG).show();
                        return;
                    } finally {
                        try {
                            inputStream.close();
                        } catch (IOException e) {

                        }
                    }
                    if (fileSize >= FILE_SIZE_LIMIT) {
                        Toast.makeText(this, getString(R.string.file_size_warning), Toast.LENGTH_LONG).show();
                        return;
                    }

                }
            } else {
                //add to gallery
                Intent mediaScanIntent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
                mediaScanIntent.setData(mMediaUri);
                sendBroadcast(mediaScanIntent);
            }

            Intent recipientIntent = new Intent(this, RecipientsActivity.class);
            recipientIntent.setData(mMediaUri);

                String fileType;
                if (requestCode == PICK_PHOTO_REQUEST || requestCode == TAKE_PHOTO_REQUEST) {
                    fileType = ParseConstants.TYPE_IMAGE;
                } else {
                    fileType = ParseConstants.TYPE_VIDEO;
                }




                recipientIntent.putExtra(ParseConstants.KEY_FILE_TYPE, fileType);
                startActivity(recipientIntent);

        }
        else if(resultCode != RESULT_CANCELED){
           Toast.makeText(this,R.string.general_error, Toast.LENGTH_LONG).show();
        }
    }

    private void GoToLogin() {
        Intent intent = new Intent(this,LoginActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
        startActivity(intent);
    }






    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.my, menu);
        return true;
    }



    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int itemId = item.getItemId();
        switch(itemId){

            case R.id.action_logout_item:
            ParseUser.logOut();
            GoToLogin();
                break;
            case R.id.action_goto_settings:
                Intent intent3 = new Intent(this, SettingsActivity.class);

                startActivity(intent3);
                break;

            case R.id.Createpicture:
                Intent intent1= new Intent(this, MotionViewsActivity.class);
                startActivity(intent1);
                break;
            case R.id.action_edit_friends:
            Intent intent = new Intent(this, EditFriendsActivity.class);
            startActivity(intent);
                break;
            case R.id.action_camera:
                AlertDialog.Builder builder = new AlertDialog.Builder(this);
                builder.setItems(R.array.camera_choices, mDialogListener);
                AlertDialog dialog = builder.create();
                dialog.show();
                break;


        //return super.onOptionsItemSelected(item);
            //default: return super.onOptionsItemSelected(item);
    }

        return super.onOptionsItemSelected(item);
    }


    @Override
    public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
        // When the given tab is selected, switch to the corresponding page in
        // the ViewPager.
        mViewPager.setCurrentItem(tab.getPosition());
    }

    @Override
    public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
    }

    @Override
    public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
    }

    @Override
    protected void onResume() {
        super.onResume();
        AppEventsLogger.activateApp(this);

    }
    @Override
    protected void onPause() {
        super.onPause();

        // Logs 'app deactivate' App Event.
        AppEventsLogger.deactivateApp(this);
    }




}

public class FriendsFragment extends Fragment {

    public static final String TAG = FriendsFragment.class.getSimpleName();

    protected List<ParseUser> mFriends;
    protected ParseRelation<ParseUser> mFriendRelation;
    protected ParseUser mCurrentUser;
    protected GridView mGridView;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.user_grid, container, false);

        mGridView = (GridView)rootView.findViewById(R.id.friendsGrid);

        TextView emptyTextView = (TextView)rootView.findViewById(android.R.id.empty);
        mGridView.setEmptyView(emptyTextView);

        return rootView;
    }

    @Override
    public void onResume() {
        super.onResume();

        mCurrentUser = ParseUser.getCurrentUser();
        mFriendRelation = mCurrentUser.getRelation(ParseConstants.KEY_FRIENDS_RELATION);

        getActivity().setProgressBarIndeterminate(true);

        ParseQuery<ParseUser> query = mFriendRelation.getQuery();
        query.addAscendingOrder(ParseConstants.KEY_USERNAME);
                query.findInBackground(new FindCallback<ParseUser>() {
            @Override
            public void done(List<ParseUser> friends, ParseException e) {
                getActivity().setProgressBarIndeterminate(false);
                if (e == null) {
                mFriends = friends;
                String[] usernames = new String[mFriends.size()];
                int i = 0;
                for (ParseUser user : mFriends) {
                    usernames[i] = user.getUsername();
                    i++;


                }
                    if(mGridView.getAdapter() == null){
                    UserAdapter adapter = new UserAdapter(getActivity(), mFriends);
                mGridView.setAdapter(adapter);}
                   else{
                        ((UserAdapter)mGridView.getAdapter()).refill(mFriends);
                    }

            }
                else {
                    Log.e(TAG, e.getMessage());
                    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
                    builder.setMessage(e.getMessage())
                            .setTitle(R.string.error_title)
                            .setPositiveButton(android.R.string.ok, null);
                    AlertDialog dialog = builder.create();
                    dialog.show();
                }
            }
        });
    }
}