App crashes whenever I log out, authentication with firebase

Question

i'm creating a sing in up and whenever i log in then log out i crash, I get this error:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.google.firebase.auth.FirebaseUser.getUid()' on a null object reference
        at net.app.MainActivity.onCreate(MainActivity.java:89)

with the line 89 being:

StorageReference profileRef = storageReference.child("users/"+fAuth.getCurrentUser().getUid()+"/profile.jpg");
        profileRef.getDownloadUrl().addOnSuccessListener(new OnSuccessListener<Uri>() {
            @Override
            public void onSuccess(Uri uri) {
                Picasso.get().load(uri).into(profileImage);
            }
        });

and the mainactivity code is: package net.smallacademy.authenticatorapp;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

import android.content.DialogInterface;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import com.google.android.gms.tasks.OnFailureListener;
import com.google.android.gms.tasks.OnSuccessListener;
import com.google.android.material.bottomnavigation.BottomNavigationView;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.firestore.DocumentReference;
import com.google.firebase.firestore.DocumentSnapshot;
import com.google.firebase.firestore.EventListener;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.FirebaseFirestoreException;
import com.google.firebase.storage.FirebaseStorage;
import com.google.firebase.storage.StorageReference;
import com.squareup.picasso.Picasso;

import javax.annotation.Nullable;

public class MainActivity extends AppCompatActivity {
    private static final int GALLERY_INTENT_CODE = 1023 ;
    TextView fullName,email,phone,verifyMsg;
    FirebaseAuth fAuth;
    FirebaseFirestore fStore;
    String userId;
    Button resendCode;
    Button resetPassLocal,changeProfileImage;
    FirebaseUser user;
    ImageView profileImage;
    StorageReference storageReference;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //initialize variable for navigation
        BottomNavigationView bottomNavigationView=findViewById(R.id.bottom_navigation);
        //set home to be selected
        bottomNavigationView.setSelectedItemId(R.id.profile);
        //preform itemselectedlistener
        bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                switch (item.getItemId()){
                    case R.id.home:
                        startActivity(new Intent(getApplicationContext(),home.class));
                        overridePendingTransition(0,0);
                        return true;
                    case R.id.profile:
                        return true;
                    case R.id.exercice:
                        startActivity(new Intent(getApplicationContext(),hi.class));
                        overridePendingTransition(0,0);
                        return true;
                }
                return false;
            }
        });
        phone = findViewById(R.id.profilePhone);
        fullName = findViewById(R.id.profileName);
        email    = findViewById(R.id.profileEmail);
        resetPassLocal = findViewById(R.id.resetPasswordLocal);

        profileImage = findViewById(R.id.profileImage);
        changeProfileImage = findViewById(R.id.changeProfile);


        fAuth = FirebaseAuth.getInstance();
        fStore = FirebaseFirestore.getInstance();
        storageReference = FirebaseStorage.getInstance().getReference();

        StorageReference profileRef = storageReference.child("users/"+fAuth.getCurrentUser().getUid()+"/profile.jpg");
        profileRef.getDownloadUrl().addOnSuccessListener(new OnSuccessListener<Uri>() {
            @Override
            public void onSuccess(Uri uri) {
                Picasso.get().load(uri).into(profileImage);
            }
        });

        resendCode = findViewById(R.id.resendCode);
        verifyMsg = findViewById(R.id.verifyMsg);


        userId = fAuth.getCurrentUser().getUid();
        user = fAuth.getCurrentUser();

        if(!user.isEmailVerified()){
            verifyMsg.setVisibility(View.VISIBLE);
            resendCode.setVisibility(View.VISIBLE);

            resendCode.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(final View v) {

                    user.sendEmailVerification().addOnSuccessListener(new OnSuccessListener<Void>() {
                        @Override
                        public void onSuccess(Void aVoid) {
                            Toast.makeText(v.getContext(), "Verification Email Has been Sent.", Toast.LENGTH_SHORT).show();
                        }
                    }).addOnFailureListener(new OnFailureListener() {
                        @Override
                        public void onFailure(@NonNull Exception e) {
                            Log.d("tag", "onFailure: Email not sent " + e.getMessage());
                        }
                    });
                }
            });
        }




        DocumentReference documentReference = fStore.collection("users").document(userId);
        documentReference.addSnapshotListener(this, new EventListener<DocumentSnapshot>() {
            @Override
            public void onEvent(@Nullable DocumentSnapshot documentSnapshot, @Nullable FirebaseFirestoreException e) {
                if(documentSnapshot.exists()){
                    phone.setText(documentSnapshot.getString("phone"));
                    fullName.setText(documentSnapshot.getString("fName"));
                    email.setText(documentSnapshot.getString("email"));

                }else {
                    Log.d("tag", "onEvent: Document do not exists");
                }
            }
        });


        resetPassLocal.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                final EditText resetPassword = new EditText(v.getContext());

                final AlertDialog.Builder passwordResetDialog = new AlertDialog.Builder(v.getContext());
                passwordResetDialog.setTitle("Reset Password ?");
                passwordResetDialog.setMessage("Enter New Password > 8 Characters long.");
                passwordResetDialog.setView(resetPassword);

                passwordResetDialog.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        // extract the email and send reset link
                        String newPassword = resetPassword.getText().toString();
                        user.updatePassword(newPassword).addOnSuccessListener(new OnSuccessListener<Void>() {
                            @Override
                            public void onSuccess(Void aVoid) {
                                Toast.makeText(MainActivity.this, "Password Reset Successfully.", Toast.LENGTH_SHORT).show();
                            }
                        }).addOnFailureListener(new OnFailureListener() {
                            @Override
                            public void onFailure(@NonNull Exception e) {
                                Toast.makeText(MainActivity.this, "Password Reset Failed.", Toast.LENGTH_SHORT).show();
                            }
                        });
                    }
                });

                passwordResetDialog.setNegativeButton("No", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        // close
                    }
                });

                passwordResetDialog.create().show();

            }
        });

        changeProfileImage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // open gallery
                Intent i = new Intent(v.getContext(),EditProfile.class);
                i.putExtra("fullName",fullName.getText().toString());
                i.putExtra("email",email.getText().toString());
                i.putExtra("phone",phone.getText().toString());
                startActivity(i);
//

            }
        });


    }



    //this is the logout function
    public void logout(View view) {
        FirebaseAuth.getInstance().signOut();//logout
        startActivity(new Intent(getApplicationContext(),Login.class));
        Toast.makeText(this,"Logging Out",Toast.LENGTH_SHORT).show();
        finish();
    }


}

I don't get why it's happening,it was working fine before

Answer 1

Before using fAuth.getCurrentUser().getUid() check if there is a user currently signed in

FirebaseUser user=FirebaseAuth.getInstance().getCurrentUser();
    if(user!=null){
            StorageReference profileRef= storageReference.child("users/"+user.getUid()+"/profile.jpg");
    
            profileRef.getDownloadUrl().addOnSuccessListener(new OnSuccessListener<Uri>(){
                @Override
                public void onSuccess(Uri uri){
                  Picasso.get().load(uri).into(profileImage);
                  }
            });
    }

That should solve the problem, but still you will have to handle a user not signed in