Empty email field of Firebase Auth User using Facebook Login Integration (Firebase 3.0)

I have successfully deployed tutorial code from https://firebase.google.com/docs/auth/android/facebook-login for integrating Firebase Auth logins with Facebook. The users successfully created in Firebase Auth console.

However, I noticed that the Email field in the user object is empty (—). Strangely, I successfully retrieved the email information directly from provider result objects using GraphRequest using the acquired token.

Based on the documentation I read (https://firebase.google.com/docs/reference/android/com/google/firebase/auth/FirebaseUser.html#getEmail()), the email field should be populated from login providers.

Some additional strange behaviour:

1. After successful login, the onAuthStateChanged is called twice. The value of firebaseAuth.getCurrentUser().getProviderId() is Firebase on both occasion
2. I try to list down the providers from the FirebaseUser object, user.getProviderData(). I got two providers: firebase and facebook.com
3. When I tried to update email using FirebaseUser.updateEmail(event.getEmail()), I got this error: An inteal error has occurred. [ EMAIL_EXISTS ]

Is there something I miss or did I do something wrong?

Here's my code:

public class LoginActivity extends AppCompatActivity {
    private static final String TAG = "LOGIN_ACTIVITY";
    private static final int RC_SIGN_IN = 777;
    private EventBus eventBus;
    private SweetAlertDialog pDialog;

    private FirebaseAuth mAuth;
    private FirebaseAuth.AuthStateListener mAuthListener;
    private CallbackManager mCallbackManager;
    private ImageView mPasswordVisibilityView;
    private TextView txtPassword;
    private boolean justEnteredAuthStateChanged = false;
    private GoogleApiClient mGoogleApiClient;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        FacebookSdk.sdkInitialize(getApplicationContext());

        setContentView(R.layout.login);

        // Firebase
        mAuth = FirebaseAuth.getInstance();

        mAuthListener = new FirebaseAuth.AuthStateListener() {
            @Override
            public void onAuthStateChanged(@NonNull final FirebaseAuth firebaseAuth) {
                final FirebaseUser user = firebaseAuth.getCurrentUser();
                if (user != null) {
                    // User is signed in
                    Util.logassert("Auth Provider = " + firebaseAuth.getCurrentUser().getProviderId()); // this is called twice, values of Provider = Firebase 
                    Util.logassert("total provider = " + user.getProviderData().size()); // output = 2. "Firebase" and "facebook.com"
                    for (int i = 0; i < user.getProviderData().size(); i++) {
                        UserInfo info = user.getProviderData().get(i);
                        Util.logassert(info.getProviderId() + ", email = " + info.getEmail()); // both empty
                        Util.logassert("current provider = " + info.getProviderId() + " - " + info);
                    }

                } else {
                    Util.logassert("onAuthStateChanged user logged out");
                }
                // ...

            }
        };
        mAuth.addAuthStateListener(mAuthListener);

        // Firebase Facebook TapAuth
        // Initialize Facebook Login button

        mCallbackManager = CallbackManager.Factory.create();

        LoginManager.getInstance().registerCallback(mCallbackManager, new FacebookCallback<LoginResult>() {
            @Override
            public void onSuccess(LoginResult loginResult) {
                Util.logassert("facebook:onSuccess:" + loginResult);
                handleFacebookAccessToken(loginResult.getAccessToken());
                Util.logassert("granted = " + loginResult.getRecentlyGrantedPermissions()); // output [email and public_profile]
                Util.logassert("denied = " + loginResult.getRecentlyDeniedPermissions());
            }

            @Override
            public void onCancel() {
                Util.logassert("facebook:onCancel");
                // ...
            }

            @Override
            public void onError(FacebookException error) {
                Util.logassert("facebook:onError" + error.getMessage());
                // ...
            }
        });

        FancyButton btnFacebook = (FancyButton) findViewById(R.id.btn_facebook_share);
        btnFacebook.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                LoginManager.getInstance().logInWithReadPermissions(LoginActivity.this, Arrays.asList("public_profile", "email"));
                Util.logassert("try facebook login");
            }
        });



        txtPassword = (EditText) findViewById(R.id.input_password);
    }



    private void handleFacebookAccessToken(AccessToken token) {
        Util.logassert("handleFacebookAccessToken:" + token);

        GraphRequest request = GraphRequest.newMeRequest(
                token,
                new GraphRequest.GraphJSONObjectCallback() {
                    @Override
                    public void onCompleted(
                            JSONObject object,
                            GraphResponse response) {
                        // Application code
                        Log.v("LoginActivity", response.toString());
                        Util.logassert("graph res = " + response.getRawResponse());

                        try {
                            /* successfully output email address from graph request here */
                            FbGraphEvent event = new FbGraphEvent(response.getJSONObject().getString("email"), response.getJSONObject().getString("name"));
                            EventBus.getDefault().postSticky(event);
                        } catch (Exception e) {
                            Log.e("MomInvoice", "Error in parsing json fb graph", e);
                        }
                    }
                });
        Bundle parameters = new Bundle();
        parameters.putString("fields", "email,name");
        request.setParameters(parameters);
        request.executeAsync();

        AuthCredential credential = FacebookAuthProvider.getCredential(token.getToken());

        mAuth.signInWithCredential(credential)
                .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        Util.logassert("signInWithCredential:onComplete:" + task.isSuccessful());


                        if (!task.isSuccessful()) {
                            Util.logassert("signInWithCredential failed coz = " + task.getException().getMessage());
                            Toast.makeText(LoginActivity.this, "Authentication failed :(",
                                    Toast.LENGTH_SHORT).show();
                        }

                    }
                });
    }


    @Override
    public void onStart() {
        super.onStart();
        Util.logassert("masuk onStart LoginActivity");
    }

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

    @Override
    protected void onDestroy() {
        if (mAuthListener != null) {
            mAuth.removeAuthStateListener(mAuthListener);
        }
        super.onDestroy();
    }

    @Override
    protected void onNewIntent(Intent intent) {
        super.onNewIntent(intent);
    }

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

        super.onActivityResult(requestCode, resultCode, data);

        if (mCallbackManager != null) {
            mCallbackManager.onActivityResult(requestCode, resultCode, data);
            Util.logassert("hasilx " + requestCode + " = " + resultCode);
        }

    }
}