java.lang.NullPointerException: Boş bir nesne başvurusu [duplicate] üzerinde sanal 'boolean java.lang.String.isEmpty ()' yöntemini çağırma girişimi

Uygulamamda bir hata var ve bunu nasıl çözeceğimi bilmiyorum. Uygulamamı çalıştırmayı denediğimde, maalesef uygulama durdu ve logcat'te şunu söylüyor:

java.lang.NullPointerException: Boş nesne başvurusunda boş nesne başvurusu üzerinde 'boolean java.lang.String.isEmpty ()' sanal yöntemini çağırma girişimi

t, kullanıcı oturum açmadığından kullanıcıyı oturum açma etkinliğine götürmesi varsayılır. Bu, hatanın işaret edildiği parçanın kodudur.

package com.app.whatsupafrica;


import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import com.firebase.ui.database.FirebaseRecyclerAdapter;
import com.firebase.ui.database.FirebaseRecyclerOptions;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.squareup.picasso.Picasso;

import de.hdodenhof.circleimageview.CircleImageView;


/**
* A simple {@link Fragment} subclass.
*/
public class ChatsFragment extends Fragment
{
private View PrivateChatsView;
private RecyclerView chatsList;

private DatabaseReference ChatsRef, UsersRef;
private FirebaseAuth mAuth;
private String currentUserID;


public ChatsFragment()
{
    // Required empty public constructor
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    PrivateChatsView = inflater.inflate(R.layout.fragment_chats, container, false);


    mAuth = FirebaseAuth.getInstance();
    currentUserID = mAuth.getUid();
    if (mAuth.getUid() == null)
    {
     SendUserToLoginActivity();
    }
    if (! mAuth.getUid().isEmpty())
    {
        ChatsRef = FirebaseDatabase.getInstance().getReference().child("Contacts").child(mAuth.getUid());
    }
    UsersRef = FirebaseDatabase.getInstance().getReference().child("Users");


    chatsList = (RecyclerView) PrivateChatsView.findViewById(R.id.chats_list);
    chatsList.setLayoutManager(new LinearLayoutManager(getContext()));


    return PrivateChatsView;
}


@Override
public void onStart()
{
    super.onStart();


    FirebaseRecyclerOptions<Contacts> options =
            new FirebaseRecyclerOptions.Builder<Contacts>()
            .setQuery(ChatsRef, Contacts.class)
            .build();


    FirebaseRecyclerAdapter<Contacts, ChatsViewHolder> adapter =
            new FirebaseRecyclerAdapter<Contacts, ChatsViewHolder>(options) {
                @Override
                protected void onBindViewHolder(@NonNull final ChatsViewHolder holder, int position, @NonNull Contacts model)
                {
                    final String usersIDs = getRef(position).getKey();
                    final String[] retImage = {"default_image"};

                    UsersRef.child(usersIDs).addValueEventListener(new ValueEventListener() {
                        @Override
                        public void onDataChange(@NonNull DataSnapshot dataSnapshot)
                        {
                            if (dataSnapshot.exists())
                            {
                                if (dataSnapshot.hasChild("image"))
                                {
                                    retImage[0] = dataSnapshot.child("image").getValue().toString();
                                    Picasso.get().load(retImage[0]).into(holder.profileImage);
                                }

                                final String retName = dataSnapshot.child("name").getValue().toString();
                                final String retStatus = dataSnapshot.child("status").getValue().toString();

                                holder.userName.setText(retName);
                                // holder.userStatus.setText("Last Seen: " + "\n" + "Date " + " Time");

                                holder.itemView.setOnClickListener(new View.OnClickListener() {
                                    @Override
                                    public void onClick(View v)
                                    {
                                        Intent chatIntent = new Intent(getContext(), ChatActivity.class);
                                        chatIntent.putExtra("visit_user_id", usersIDs);
                                        chatIntent.putExtra("visit_user_name", retName);
                                        chatIntent.putExtra("visit_image", retImage[0]);
                                        startActivity(chatIntent);
                                    }
                                });
                            }
                        }

                        @Override
                        public void onCancelled(@NonNull DatabaseError databaseError) {

                        }
                    });
                }

                @NonNull
                @Override
                public ChatsViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i)
                {
                    View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.users_display_layout, viewGroup, false);
                    return new ChatsViewHolder(view);
                }
            };

    chatsList.setAdapter(adapter);
    adapter.startListening();
}




public static class ChatsViewHolder extends RecyclerView.ViewHolder
{
    CircleImageView profileImage;
    TextView userStatus, userName;


    public ChatsViewHolder(@NonNull View itemView)
    {
        super(itemView);

        profileImage = itemView.findViewById(R.id.users_profile_image);
        userStatus = itemView.findViewById(R.id.user_status);
        userName = itemView.findViewById(R.id.user_profile_name);
    }
}
private void SendUserToLoginActivity()
{
    Intent loginIntent = new Intent(getContext(), LoginActivity.class);
    startActivity(loginIntent);
}
}

Kullanıcının oturum açıp açmadığını kontrol edin

 if(! Objects.requireNonNull( mAuth.getUid() ).isEmpty())
     currentUserID = mAuth.getUid();
 else
     //sign in the user 

Bu kodu ekleyin:

mAuth.getUid();

onun yerine

mAuth.getCurrentUser().getUid();

Görünüşe göre mevcut kullanıcı boş