Why do i get argument might be null error?

Question

package e.starf.project;

import android.content.Context;
import android.content.Intent;
import android.media.Image;
import android.support.annotation.NonNull;
import android.support.design.widget.NavigationView;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.Toolbar;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.RecyclerView;
import android.view.Display;
import android.view.LayoutInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;

import com.bumptech.glide.annotation.GlideModule;
import com.bumptech.glide.module.AppGlideModule;
import com.bumptech.glide.Glide;
import com.firebase.ui.database.FirebaseRecyclerAdapter;
import com.firebase.ui.database.FirebaseRecyclerOptions;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
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.google.firebase.storage.FirebaseStorage;
import com.google.firebase.storage.StorageReference;
import com.squareup.picasso.Picasso;

import de.hdodenhof.circleimageview.CircleImageView;

public class MainActivity extends AppCompatActivity {
    private NavigationView navigationView;
    private DrawerLayout drawerLayout;
    private ActionBarDrawerToggle actionBarDrawerToggle;
    private RecyclerView postList;
    private Toolbar toolbar;
    private ImageButton AddNewPostButton;
    private FirebaseAuth firebaseAuth;
    private DatabaseReference UsersRef, PostsRef, LikesRef;
    private StorageReference mStorageRef;

    String currentUserID;
    Boolean LikeChecker = false;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);



        firebaseAuth = FirebaseAuth.getInstance();
        UsersRef = FirebaseDatabase.getInstance().getReference().child("Users");
        PostsRef = FirebaseDatabase.getInstance().getReference().child("Posts");
        LikesRef = FirebaseDatabase.getInstance().getReference().child("Likes");

        UsersRef.keepSynced(true);
        PostsRef.keepSynced(true);
        LikesRef.keepSynced(true);
        mStorageRef = FirebaseStorage.getInstance().getReference();

        toolbar = (Toolbar) findViewById(R.id.main_page_toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("Home");

        AddNewPostButton = (ImageButton) findViewById(R.id.add_new_post);

        drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        actionBarDrawerToggle = new ActionBarDrawerToggle(MainActivity.this, drawerLayout,
            R.string.drawer_open, R.string.drawer_close);
        drawerLayout.addDrawerListener(actionBarDrawerToggle);
        actionBarDrawerToggle.syncState();
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        navigationView = (NavigationView) findViewById(R.id.navigation_view);

        postList = (RecyclerView) findViewById(R.id.all_users_post_list);
        postList.setHasFixedSize(true);
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
        linearLayoutManager.setReverseLayout(true);
        linearLayoutManager.setStackFromEnd(true);
        postList.setLayoutManager(linearLayoutManager);

        View navView = navigationView.inflateHeaderView(R.layout.navigration_header);

        navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                UserMenuSelector(item);
                return false;
            }
        });

        AddNewPostButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                SendUserToPostActivity();
            }
        });
        DisplayAllUsersPosts();
    }

    private void DisplayAllUsersPosts() {
        final FirebaseRecyclerOptions < Posts options = new FirebaseRecyclerOptions.Builder < Posts().setQuery(PostsRef,
            Posts.class).build();

        FirebaseRecyclerAdapter < Posts, PostsViewHolder firebaseRecyclerAdapter = new FirebaseRecyclerAdapter < Posts,
            PostsViewHolder(options) {
                @NonNull
                @Override
                public PostsViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {

                    View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.all_posts_layout,
                        viewGroup, false);
                    return new PostsViewHolder(view);
                }

                @Override
                protected void onBindViewHolder(@NonNull final PostsViewHolder holder, int position, @NonNull final Posts model) {
                    final String PostKey = getRef(position).getKey();

                    holder.setName(model.getName());
                    holder.setTime(model.getTime());
                    holder.setDate(model.getDate());
                    holder.setDescription(model.getDescription());
                    holder.setPostimage(getApplicationContext(), model.getPostimage());

                    holder.setLikeButtonStatus(PostKey);

                    holder.mView.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View view) {
                            Intent clickPostIntent = new Intent(MainActivity.this, ClickPostActivity.class);
                            clickPostIntent.putExtra("PostKey", PostKey);
                            startActivity(clickPostIntent);
                        }
                    });

                    holder.CommentPostButton.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View view) {
                            Intent clickPostIntent = new Intent(MainActivity.this, CommentsActivity.class);
                            clickPostIntent.putExtra("PostKey", PostKey);
                            startActivity(clickPostIntent);
                        }
                    });

                    holder.LikePostButton.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View view) {
                            LikeChecker = true;

                            if (LikeChecker) {
                                LikesRef.addValueEventListener(new ValueEventListener() {
                                    @Override
                                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                                        if (LikeChecker.equals(true)) {
                                            if (dataSnapshot.child(PostKey).hasChild(currentUserID)) {
                                                LikesRef.child(PostKey).child(currentUserID).removeValue();
                                                LikeChecker = false;
                                            } else {
                                                LikesRef.child(PostKey).child(currentUserID).setValue(true);
                                                LikeChecker = false;
                                            }
                                        }

                                    }

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

                                    }
                                });


                            }

                        }
                    });

                }
            };
        postList.setAdapter(firebaseRecyclerAdapter);
        firebaseRecyclerAdapter.startListening();
    }

    public static class PostsViewHolder extends RecyclerView.ViewHolder {
        View mView;
        ImageButton LikePostButton, CommentPostButton;
        TextView DisplayNoOfLikes;
        int countLikes;
        String currentUserID;
        DatabaseReference LikesRef;

        public PostsViewHolder(@NonNull View itemView) {
            super(itemView);
            mView = itemView;

            LikePostButton = (ImageButton) mView.findViewById(R.id.like_button);
            CommentPostButton = (ImageButton) mView.findViewById(R.id.comment_button);
            DisplayNoOfLikes = (TextView) mView.findViewById(R.id.display_no_of_likes);

            LikesRef = FirebaseDatabase.getInstance().getReference().child("Likes");
            currentUserID = FirebaseAuth.getInstance().getCurrentUser().getUid();
        }

        public void setLikeButtonStatus(final String PostKey) {
            LikesRef.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    if (dataSnapshot.child(PostKey).hasChild(currentUserID)) {
                        countLikes = (int) dataSnapshot.child(PostKey).getChildrenCount();
                        LikePostButton.setImageResource(R.drawable.like);
                        DisplayNoOfLikes.setText(Integer.toString(countLikes) + (" Likes"));
                    } else {
                        countLikes = (int) dataSnapshot.child(PostKey).getChildrenCount();
                        LikePostButton.setImageResource(R.drawable.dislike);
                        DisplayNoOfLikes.setText(Integer.toString(countLikes) + (" Likes"));

                    }
                }


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

                }
            });

        }
        public void setName(String name) {
            TextView username = (TextView) mView.findViewById(R.id.post_user_name);
            username.setText(name);
        }
        public void setTime(String time) {
            TextView PostTime = (TextView) mView.findViewById(R.id.post_time);
            PostTime.setText(" " + time);
        }
        public void setDate(String date) {
            TextView PostDate = (TextView) mView.findViewById(R.id.post_date);
            PostDate.setText(" " + date);
        }
        public void setDescription(String description) {
            TextView PostDescription = (TextView) mView.findViewById(R.id.post_question);
            PostDescription.setText(description);
        }
        public void setPostimage(Context ctx, String postimage) {
            ImageView PostImage = (ImageView) mView.findViewById(R.id.post_image);
            Picasso.get().load(postimage).into(PostImage);
            //   Glide.with(ctx).load(postimage).into(PostImage);
        }
    }


    private void SendUserToPostActivity() {
        Intent addNewPostIntent = new Intent(MainActivity.this, PostActivity.class);
        startActivity(addNewPostIntent);
    }

    protected void onStart() {
        super.onStart();

        FirebaseUser currentUser = firebaseAuth.getCurrentUser();

        if (currentUser == null) {
            SendUserToLoginActivity();
        } else {
            CheckUserExistence();
        }
    }

    private void CheckUserExistence() {
        final String current_user_id = firebaseAuth.getCurrentUser().getUid();
        UsersRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                if (!dataSnapshot.hasChild(current_user_id)) {
                    SendUserToSetupActivity();
                }
            }

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

            }
        });
    }

    private void SendUserToSetupActivity() {
        Intent setupIntent = new Intent(MainActivity.this, SetupActivity.class);
        setupIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
        startActivity(setupIntent);
        finish();
    }

    private void SendUserToLoginActivity() {
        Intent loginIntent = new Intent(MainActivity.this, LoginActivity.class);
        loginIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
        startActivity(loginIntent);
        finish();
    }

    private void SendUserToProfileActivity() {
        Intent profileIntent = new Intent(MainActivity.this, ProfileActivity.class);
        startActivity(profileIntent);
    }

    private void SendUserToAboutUsActivity() {
        Intent AboutUsIntent = new Intent(MainActivity.this, AboutUs.class);
        startActivity(AboutUsIntent);
    }
    private void SendUserToContactUsActivity() {
        Intent AboutUsIntent = new Intent(MainActivity.this, ContactUs.class);
        startActivity(AboutUsIntent);
    }

    public boolean onOptionsItemSelected(MenuItem item) {
        if (actionBarDrawerToggle.onOptionsItemSelected(item)) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    private void UserMenuSelector(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.nav_post:
                SendUserToPostActivity();
                break;
            case R.id.nav_menu1:
                Toast.makeText(this, "Home", Toast.LENGTH_SHORT).show();
                break;
            case R.id.nav_menu2:
                Toast.makeText(this, "Discussion FOrum", Toast.LENGTH_SHORT).show();
                break;
            case R.id.nav_menu3:
                SendUserToProfileActivity();
                break;
            case R.id.nav_menu4:
                SendUserToAboutUsActivity();
                break;
            case R.id.nav_menu5:
                Intent sendIntent = new Intent();
                sendIntent.setAction(Intent.ACTION_SEND);
                sendIntent.putExtra(Intent.EXTRA_TEXT, "PICT Placement.\n Forum to create awareness...\nLink:
                    https: //github.com/pragyagupta1898");
                    sendIntent.setType("text/plain"); startActivity(sendIntent); Toast.makeText(this, "Share", Toast.LENGTH_SHORT).show();
                    break;
                    case R.id.nav_contact:
                        SendUserToContactUsActivity();
                        break;
                    case R.id.nav_logout:
                        firebaseAuth.signOut(); SendUserToLoginActivity();
                        break;

                }
        }
    }

The error is here:

if(dataSnapshot.child(PostKey).hasChild(currentUserID)) 

It says:

Argument 'PostKey' might be null less... (Ctrl+F1) This inspection analyzes method control and data flow to report possible conditions that are always true or false, expressions whose value is statically proven to be constant, and situations that can lead to nullability contract violations. Variables, method parameters and return values marked as @Nullable or @NotNull are treated as nullable (or not-null, respectively) and used during the analysis to check nullability contracts, e.g. report NullPointerException (NPE) errors that might be produced. More complex contracts can be defined using @Contract annotation, for example: @Contract(", null - null") — method returns null if its second argument is null @Contract(", null - null; _, !null - !null") — method returns null if its second argument is null and not-null otherwise @Contract("true - fail") — a typical assertFalse method which throws an exception if true is passed to it The inspection can be configured to use custom @Nullable @NotNull annotations (by default the ones from annotations.jar will be used)

How to resolve it?

Answer 1

If you debug your app at this warning you will found that the mUserID = null, so you just need to inti it:

mUserID = mAuth.getCurrentUser().getUid();

Answer 2

try something like this.

if((PostKey != null) && dataSnapshot.child(PostKey).hasChild(currentUserID)) 

You can also write it so that you handle the null case

if (PostKey == null)  //do somthing
else if (dataSnapshot.child(PostKey).hasChild(currentUserID)) //do something
else //do something

Answer 3

That's not an error, it's a warning.

Since it doesn't seem that you read the warning you quoted, I'll paraphrase:

The DataSnapshot.child() method has a @Nullable flag, meaning it's possible that it will return null. Since you are calling something directly on the result of that method, Android Studio is simply telling you that, since child() can be null, running hasChild() on it might lead to a NullPointerException.

Either check the null state or ignore it.