BottomNavigationView with shifModeDisable and Badge

attrs.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="custom_navigation_bottom_bar">
        <attr name="badge" format="reference" />
    </declare-styleable>
</resources>

CustomBottomNavigationView.java

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.drawable.Drawable;
import android.support.design.internal.BottomNavigationItemView;
import android.support.design.internal.BottomNavigationMenuView;
import android.support.design.widget.BottomNavigationView;
import android.util.AttributeSet;
import android.util.Log;
import android.util.SparseArray;
import android.view.Gravity;
import android.view.View;
import android.widget.FrameLayout;
import android.widget.TextView;

import com.your.package.R;
import com.your.package.UIUtils;

import java.lang.reflect.Field;

public class CustomBottomNavigationView extends BottomNavigationView {

    //Value position for badge
    final SparseArray<Integer> badgePositionValue = new SparseArray<Integer>();

    private Drawable mDrawableBadge;

    //see guideline https://material.io/guidelines/components/bottom-navigation.html#bottom-navigation-specs
    private final int PX_MAX_ITEM_WIDTH = UIUtils.convertDpToPx(getContext(),168); //check  if 169 is better in despite of guideline, getwidth() return 169

    public CustomBottomNavigationView(Context context, AttributeSet attrs) {
        super(context, attrs);
        TypedArray a = context.obtainStyledAttributes(attrs,R.styleable.custom_navigation_bottom_bar);
        mDrawableBadge = a.getDrawable(R.styleable.custom_navigation_bottom_bar_badge);
        a.recycle();
    }

    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        // Adding badges to each Item
        BottomNavigationMenuView menuView = getBottomMenuView();
        for (int i = 0; i < menuView.getChildCount(); i++) {
            BottomNavigationItemView item = (BottomNavigationItemView) menuView.getChildAt(i);

            int width = UIUtils.convertDpToPx(getContext(), 16);
            int heigth = width;

            //Inflate TextView badge
            TextView textView = (TextView) View.inflate(getContext(), R.layout.navbar_badge_count, null);
            textView.setVisibility(GONE);
            textView.setMinimumWidth(width);
            int padding = UIUtils.convertDpToPx(getContext(), 3);
            textView.setPadding(padding, 0, padding, 0);
            //Build Layout Param of badge
            FrameLayout.LayoutParams layoutParam = new FrameLayout.LayoutParams(FrameLayout.LayoutParams.WRAP_CONTENT, heigth);
            layoutParam.gravity = Gravity.END;
            int screenWitdh = UIUtils.getDeviceWidth(getContext());
            screenWitdh = screenWitdh > PX_MAX_ITEM_WIDTH* menuView.getChildCount() ?PX_MAX_ITEM_WIDTH* menuView.getChildCount():screenWitdh ;
            int marginTop =  UIUtils.convertDpToPx(getContext(), 10);
            int marginRight = (int)(((screenWitdh / menuView.getChildCount())* 0.5)-marginTop*1.8);
            layoutParam.setMargins(0, marginTop,marginRight , 0);
            //Add it to the item
            item.addView(textView, layoutParam);

        }
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        disableShiftingMode();
        calculateBadgesPosition();
    }

    public void disableShiftingMode(){
        //This disables the shifting mode (which makes tab grow on select)
        BottomNavigationMenuView menuView = getBottomMenuView();
        try {
            Field shiftingMode = menuView.getClass().getDeclaredField("mShiftingMode");
            shiftingMode.setAccessible(true);
            shiftingMode.setBoolean(menuView, false);
            shiftingMode.setAccessible(false);
            for (int i = 0; i < menuView.getChildCount(); i++) {
                BottomNavigationItemView item = (BottomNavigationItemView) menuView.getChildAt(i);
                //noinspection RestrictedApi
                item.setShiftingMode(false);
                // set once again checked value, so view will be updated
                //noinspection RestrictedApi
                item.setChecked(item.getItemData().isChecked());
            }
        } catch (NoSuchFieldException e) {
            Log.e("BNVHelper", "Unable to get shift mode field", e);
        } catch (IllegalAccessException e) {
            Log.e("BNVHelper", "Unable to change value of shift mode", e);
        }
    }

    // allow to get the BottomMenuView
    private BottomNavigationMenuView getBottomMenuView() {
        Object menuView = null;
        try {
            Field field = BottomNavigationView.class.getDeclaredField("mMenuView");
            field.setAccessible(true);
            menuView = field.get(this);
        } catch (NoSuchFieldException e) {
            //   Crashlytics.logException(e);
        } catch (IllegalAccessException e) {
            // Crashlytics.logException(e);
        }

        return (BottomNavigationMenuView) menuView;
    }

    /**
     * This method place dynamically badge on the bottom bar
     * Since the  MenuItemCompat.getActionView() /  MenuItemCompat.setActionView() is not well supported
     * see more : http://techqa.info/programming/question/42087027/badge-on-bottomnavigationview
     * TODO each new Version of BottomNavigationView Check if this ActionView behaviour is fixed
     */
    private void calculateBadgesPosition() {
        //Manage display of badges
        BottomNavigationMenuView menuView = getBottomMenuView();
        for (int i = 0; i < menuView.getChildCount(); i++) {
            BottomNavigationItemView item = (BottomNavigationItemView) menuView.getChildAt(i);
            //noinspection RestrictedApi
            Integer value = badgePositionValue.get(i);
            TextView badge = (TextView) item.findViewById(R.id.bottom_bar_badge_id);
            if (badge != null) {
                setBadge(badge, value);
                if (mDrawableBadge != null) {
                    Drawable drawable = mDrawableBadge.getConstantState() != null ? mDrawableBadge.getConstantState().newDrawable() : null;
                    badge.setBackground(drawable);
                }
            }
        }
    }

    private void setBadge(TextView badge, Integer count) {
        //set Value
        if (count != null && count > 0) {
            badge.setText(String.valueOf(count));
            badge.setVisibility(VISIBLE);
        } else {
            badge.setVisibility(GONE);
        }
    }

    public void setBadgePositionValue(int position, int count) {
        badgePositionValue.put(position, count);
        //refresh badges
        calculateBadgesPosition();
    }

    //this is used to programmatically select a tab.
    public boolean setSelected(int index) {
        boolean success = false;
        final BottomNavigationMenuView menu = getBottomMenuView();
        if (menu.getChildCount() > index) {
            final View item = menu.getChildAt(index);
            if (item != null && item instanceof BottomNavigationItemView) {
                success = item.performClick();
            }
        }
        return success;
    }
}

layout.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                xmlns:app="http://schemas.android.com/apk/res-auto"
                android:layout_width="match_parent"
                android:layout_height="match_parent"">
    <com.your.package.common.ui.CustomBottomNavigationView
        android:id="@+id/bnv_main"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        app:badge="@drawable/your_drawable"
        app:itemIconTint="@drawable/your_drawable_selector"
        app:itemTextColor="@drawable/your_drawable_selector" />
</RelativeLayout>

Field field = BottomNavigationView.class.getDeclaredField("mMenuView");
This line is returning null. How can i resolve this error