Email string is always NULL

BrowseFragment.java

public class BrowseFragment extends TiFragment<BrowsePresenter, BrowseView> implements BrowseView, BrowseAdapter.ClickListener{

    int RC_SIGN_IN = 100;
    BrowseAdapter mBrowseAdapter;
    GridLayoutManager layoutManager;

    @BindView(R.id.progress)
    ProgressBar mProgress;
    @BindView(R.id.list)
    RecyclerView mItemRecycler;
    @BindView(R.id.bmb)
    BoomMenuButton bmb;

    @NonNull
    @Override
    public BrowsePresenter providePresenter() {
        return new BrowsePresenter();
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setRetainInstance(true);
    }

    @Override
    public View onCreateView(LayoutInflater inflater,
                             ViewGroup container,
                             Bundle savedInstanceState) {
        View fragmentView = inflater.inflate(R.layout.fragment_browse, container, false);
        ButterKnife.bind(this, fragmentView);
        setupViews();
        initBoomButton();
        return fragmentView;
    }
   
    @Override
    public void onCartAdd(Product item) {
        providePresenter().addToCart(item, 1);  // calling the presenter!
    }

    @Override
    public void onCartRemove(Product item) {
        providePresenter().addToCart(item, 0);
    }

    @Override
    public void onItemQuantity(Product item, float quantity) {
        providePresenter().addToCart(item, quantity);
    }

BrowsePresenter.java

package me.arulnadhan.grocerycorecommon.ui.browse;

import android.support.annotation.NonNull;

import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.Query;
import com.google.firebase.database.ServerValue;
import com.kelvinapps.rxfirebase.RxFirebaseAuth;
import com.kelvinapps.rxfirebase.RxFirebaseDatabase;

import net.grandcentrix.thirtyinch.TiPresenter;
import net.grandcentrix.thirtyinch.rx.RxTiPresenterSubscriptionHandler;

import java.util.ArrayList;
import java.util.List;

import me.arulnadhan.grocerycorecommon.data.model.Customer;
import me.arulnadhan.grocerycorecommon.data.model.Product;
import me.arulnadhan.grocerycorecommon.utils.Helper;
import timber.log.Timber;

/**
 * Created by AruLNadhaN on 10/12/2016.
 */

public class BrowsePresenter extends TiPresenter<BrowseView> {

    private RxTiPresenterSubscriptionHandler rxHelper = new RxTiPresenterSubscriptionHandler(this);

    private FirebaseDatabase mFirebaseDatabase = FirebaseDatabase.getInstance();
    private FirebaseAuth mFirebaseAuth = FirebaseAuth.getInstance();
    private DatabaseReference mDatabase = mFirebaseDatabase.getReference();
    private DatabaseReference mUserDB = mFirebaseDatabase.getReference().child("customers");
    private DatabaseReference mProdDB = mFirebaseDatabase.getReference().child("S01/Products");
    private Query mRef;
    private DatabaseReference cartRef;
    private FirebaseUser mUser;

    private String selectedCat, Email;

    private final List<Product> ProdList = new ArrayList<>();

    @Override
    protected void onAttachView(@NonNull BrowseView view) {
        super.onAttachView(view);
        authenticate();
        getProducts();
    }

     private void getProducts() {
        final BrowseView view = getView();
        view.showMessageLayout(false);
        view.showProgress();

        mRef = mProdDB.child("C01");
        rxHelper.manageSubscription(
                RxFirebaseDatabase.observeValueEvent(mRef,
                        dataSnapshot -> {
                            List<Product> mProd = new ArrayList<>();
                            for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                                Product Prod = Product.create(postSnapshot);
                                mProd.add(Prod);
                            }
                            return mProd;
                        })
                        .subscribe(mProd -> {
                            view.hideProgress();
                            Timber.d(mProd.get(0).productName());
                            view.showItems(mProd);
                        })
        );
    }

    public void addToCart(Product item, float quantity) {
        Timber.d("Email >> "+ Email); // Email is always NULL
    }

    private void authenticate() {
        Timber.d("AUTH Listener");
        rxHelper.manageViewSubscription(
                RxFirebaseAuth.observeAuthState(mFirebaseAuth)
                        .subscribe(firebaseUser -> {
                            if (firebaseUser != null) {
                                mUser = firebaseUser;
                                Email = firebaseUser.getEmail();
                                Timber.d("Email >> "+ Email); // Email is returned correctly!
                                Timber.d("user Photo: " + firebaseUser.getPhotoUrl());
                            } else {
                                Timber.d("TOKEN NULL");
                                sendToView(BrowseView::showLogin);
                            }
                        })
        );
    }
}