Android : I want user to select an image in navigation drawer

What I have and What I want

I have an activity with navigation drawer. In this navigation drawer, I have used ListView with BaseAdapter class. I have 2 viewTypes, the 1st row that have an Imageview. and all other rows with simple text.

Here is my Adapter Class :

public class drawer_list_adapter extends BaseAdapter {

Context context;
String[] nv_items;
int pic;
LayoutInflater layoutInflater;

public drawer_list_adapter(Context context, String[] nv_items, int pic) {
    this.context = context;
    this.nv_items = nv_items;
    this.pic = pic;
    this.layoutInflater = LayoutInflater.from(context);
  }

@Override
public int getCount() {
    return 4;
  }

@Override
public Object getItem(int position) {
    return position;
  }

@Override
public long getItemId(int position) {
    return 0;
  }

@Override
public int getViewTypeCount() {
    return 4;
  }

@Override
public int getItemViewType(int position) {
    return position;
  }

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    ViewHolder dLI;

    if (convertView == null) {
        if (getItemViewType(position) == 0){
            convertView = layoutInflater.inflate(R.layout.drawer_pro_pic, parent, false);
            dLI = new ViewHolder();
            convertView.setTag(dLI);
            dLI.avatar = (ImageView) convertView.findViewById(R.id.imageView);
            dLI.avatar.setImageResource(pic);


        }
         else {
            convertView = layoutInflater.inflate(R.layout.drawer_list_item, parent, false);
            dLI = new ViewHolder();
            convertView.setTag(dLI);
            dLI.items = (TextView) convertView.findViewById(R.id.drawer_list_text);
            dLI.items.setText(nv_items[position]);
        }
    }
    else {
        dLI = (ViewHolder) convertView.getTag();
    }

    return convertView;
}

public class ViewHolder {
    TextView items;
    ImageView avatar;
     }
  }

Now, in my main activity, i have set adapter and all that stuff. I have also defined arraystring for the 3 rows that have textview.

Here is my onCreate() method (only that part which is concerned with my issue):

    drawerLayout = (DrawerLayout) findViewById(R.id.NvDrawer);
    drawerList = (ListView) findViewById(R.id.drawer_list);
    drawer_list_adapter drawerListAdapter = new drawer_list_adapter(this, nv_items, pic);
    drawerList.setAdapter(drawerListAdapter);
    drawerList.setOnItemClickListener(new DrawerItemClickListener());

Now about the imageview (the first row), I want user to choose a pic from the gallery. i used startActivityForResult which is called when item is selected in the listview (position == 0 in my case). I can open the Gallery, but when i select the pic, the app crashes.

Below is my code for startActivitForResult and onActivityResult :

public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {

        if (position == 0){
            Intent pickFromGallery = new Intent(Intent.ACTION_PICK, MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
            startActivityForResult(pickFromGallery, OpenGallery);
        }
    }
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
      if (requestCode == OpenGallery && resultCode == RESULT_OK){
            Uri pickedImage = data.getData();
            String[] filePath = {MediaStore.Images.Media.DATA};
            Cursor cursor = getContentResolver().query(pickedImage, filePath, null, null, null);
            cursor.moveToFirst();
            String imagePath = cursor.getString(cursor.getColumnIndex(filePath[0]));
            pro_pic.setImageBitmap(BitmapFactory.decodeFile(imagePath));
            cursor.close();
        }
    }

And here is the error code :

java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1, result=-1, data=Intent { dat=content://media/external/images/media/1019 flg=0x1 }} to activity {com.hirak.assistere_doit/com.hirak.assistere_doit.do_it_main_screen}: java.lang.NullPointerException
        at android.app.ActivityThread.deliverResults(ActivityThread.java:3351)
        at android.app.ActivityThread.handleSendResult(ActivityThread.java:3394)
        at android.app.ActivityThread.access$1300(ActivityThread.java:135)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1244)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5001)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.NullPointerException
        at com.hirak.assistere_doit.do_it_main_screen.onActivityResult(do_it_main_screen.java:116)
        at android.app.Activity.dispatchActivityResult(Activity.java:5423)
        at android.app.ActivityThread.deliverResults(ActivityThread.java:3347)
        at android.app.ActivityThread.handleSendResult(ActivityThread.java:3394)
        at android.app.ActivityThread.access$1300(ActivityThread.java:135)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1244)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5001)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
        at dalvik.system.NativeStart.main(Native Method)