title: java.util.ArrayList.size()' on a null object reference
body: <p>I want to pull data from my Firebase database. My table name is "cardornek". And I set the permissions for read/write. </p>
  
  <p>But I get this "java.util.ArrayList.size()' on a null object reference" error. Any idea?</p>
  
  <p><strong>RecyclerViewAdapter.java</strong></p>
  
  <pre><code>public class RecyclerViewAdapter extends RecyclerView.Adapter&lt;RecyclerViewAdapter.ViewHolder&gt; {
  
  private ArrayList&lt;String&gt; values=null;
  RecyclerViewAdapter(ArrayList&lt;String&gt; values) {
      this.values = values;
  }
  @Override
  public RecyclerViewAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
      return new ViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.recycler_view_item,parent,false));
  }
  
  
  @Override
  public void onBindViewHolder(RecyclerViewAdapter.ViewHolder holder, int position)
  {
      holder.name.setText(values.get(position));
  }
  
  @Override
  public int getItemCount() {
      return values.size();
  }
  
  public class ViewHolder extends RecyclerView.ViewHolder
  {
      private TextView name;
      ViewHolder(View itemView) {
          super(itemView);
          name = (TextView) itemView.findViewById(R.id.list_item_text);
      }
  }
  </code></pre>
  
  <p><strong>MainActivity.java</strong></p>
  
  <pre><code>public class MainActivity extends AppCompatActivity {
  private RecyclerView recyclerView;
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
      recyclerView.setHasFixedSize(true);
      recyclerView.setLayoutManager(new LinearLayoutManager(this));
      new GetDataFromFirebase().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
  
      // Read from the database
      FirebaseDatabase database = FirebaseDatabase.getInstance();
      DatabaseReference myRef = database.getReference("cardornek");
  
      myRef.addValueEventListener(new ValueEventListener() {
  
  
          @Override
          public void onDataChange(DataSnapshot dataSnapshot) {
              ArrayList&lt;String&gt; values = (ArrayList&lt;String&gt;) dataSnapshot.getValue();
              recyclerView.setAdapter(new RecyclerViewAdapter(values));
          }
  
          @Override
          public void onCancelled(DatabaseError databaseError) {
              System.out.println("Failed to read value." + databaseError.toException());
          }
      });
  </code></pre>