Вызов функции и NULL reference

    
public class MainActivity extends AppCompatActivity {
 
    private RecyclerView rvFeed;
 protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        rvFeed = (RecyclerView) findViewById(R.id.rvFeed);
    }
public void setupFeed() {
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this) {
            @Override
            protected int getExtraLayoutSpace(RecyclerView.State state) {
                return 300;
            }
        };
        rvFeed.setLayoutManager(linearLayoutManager);
        FeedAdapter feedAdapter = new FeedAdapter(this);
        rvFeed.setAdapter(feedAdapter);
        feedAdapter.updateItems();
    }
}

class FeedAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
 
    ImageView ivFeedCenter;
    private Context context;
    private int itemsCount = 0;
    
    FeedAdapter(Context context) {
        this.context = context;
    }
 
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        final View view = LayoutInflater.from(context).inflate(R.layout.item_feed, parent, false);
        ivFeedCenter = (ImageView)view.findViewById(R.id.ivFeedCenter);
        return new CellFeedViewHolder(view);
    }
 
    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
        final CellFeedViewHolder holder = (CellFeedViewHolder) viewHolder;
        bindDefaultFeedItem(position, holder);
    }
    private void bindDefaultFeedItem(int position, CellFeedViewHolder holder) {
        if (position == 0) {
            Picasso.with(context).load("").into(ivFeedCenter);
       } else if(position == 1) {
            Picasso.with(context).load("").into(ivFeedCenter);
        }
        else if(position == 2){
 
            Picasso.with(context).load("").into(ivFeedCenter);
        }
        holder.btnComments.setTag(position);
    }
 
    void updateItems() {
        itemsCount = 3;
        notifyDataSetChanged();
    }
 
    @Override
    public int getItemViewType(int position) {
        return 1;
    }
 
    @Override
    public int getItemCount() {
        return itemsCount;
    }
 
    private static class CellFeedViewHolder extends RecyclerView.ViewHolder {
 
        ImageButton btnComments;
        ImageButton btnLike;
        ImageButton btnMore;
        TextSwitcher tsLikesCounter;
        ImageView ivUserProfile;
        FrameLayout vImageRoot;
        CellFeedViewHolder(View view) {
            super(view);
            btnComments = (ImageButton) view.findViewById(R.id.btnComments);
            btnLike = (ImageButton) view.findViewById(R.id.btnLike);
            vImageRoot = (FrameLayout) view.findViewById(R.id.vImageRoot);
        }
    }
 
}

public class MenuListFragment extends Fragment {
 private FlowingDrawer mDrawer;
//    MainActivity ma;
 
 
    private ImageView ivMenuUserProfilePhoto;
 
    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }
 
 
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_menu, container,
                false);
 
        ivMenuUserProfilePhoto = (ImageView) view.findViewById(R.id.ivMenuUserProfilePhoto);
        final NavigationView vNavigation = (NavigationView) view.findViewById(R.id.vNavigation);
        vNavigation.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
 
            @Override
            public boolean onNavigationItemSelected(MenuItem menuItem) {
                int id = menuItem.getItemId();
 
                switch (id) {
//                    case R.id.gothic1:
//                        ma.setupFeed();
//                        break;
//                    case R.id.gothic2:
//                        ma.setupFeed2();
//                        break;
                }
                        return true;
 
//                Toast.makeText(getActivity(),menuItem.getTitle(),Toast.LENGTH_SHORT).show();
//                return false;
            }
        });
        setupHeader();
        return view ;
    }
 
    private void setupHeader() {
        int avatarSize = getResources().getDimensionPixelSize(R.dimen.global_menu_avatar_size);
        String profilePhoto = getResources().getString(R.string.user_profile_photo);
        Picasso.with(getActivity())
                .load(profilePhoto)
                .placeholder(R.drawable.img_circle_placeholder)
                .resize(avatarSize, avatarSize)
                .centerCrop()
                .transform(new CircleTransformation())
                .into(ivMenuUserProfilePhoto);
    }
 
}