Error while generating new objects in ListView. (ListView null object reference)

In logcat i'm getting this information: "java.lang.NullPointerException: Attempt to invoke interface method 'int

java.util.List.size()' on a null object reference"
package com.example.kuba.seriale;
import android.content.Context;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.ListView;
import android.widget.SearchView;
import android.widget.TextView;
import com.example.kuba.seriale.models.MovieModel;
import java.util.List;
public class MainActivity extends AppCompatActivity {
    SearchView src;
    Button btn;
    private TextView txv;
    ListView lvm;
    String api_key = "***************";
    JSONTasks json = new JSONTasks();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        src = (SearchView) findViewById(R.id.searchView);
        txv = (TextView) findViewById(R.id.textView);
        btn = (Button) findViewById(R.id.button);
        lvm = (ListView)findViewById(R.id.lvMovies);



        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String zapytanie = src.getQuery().toString();
                if((zapytanie==null)||(zapytanie=="")){
                    zapytanie = "Homeland";
                }
                String Link = "http://api.themoviedb.org/3/search/tv?query="+zapytanie+"&api_key="+api_key;

                MovieAdapter movieAdapter = new MovieAdapter(getApplicationContext(), R.layout.row, json.mvc(Link));
                try{
                    lvm.setAdapter(movieAdapter);
                } catch (Exception e){
                    txv.setText(e.getMessage());
                }



            }
        });
        src.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
            @Override
            public boolean onQueryTextSubmit(String query) {

                return false;
            }

            @Override
            public boolean onQueryTextChange(String newText) {


                return false;
            }
        });
    }
    public void Search(){
        String zapytanie = src.getQuery().toString();
        if((zapytanie==null)||(zapytanie=="")){
            zapytanie = "Homeland";
        }
        String Link = "http://api.themoviedb.org/3/search/tv?query="+zapytanie+"&api_key="+api_key;
        MovieAdapter movieAdapter = new MovieAdapter(getApplicationContext(), R.layout.row, json.mvc(Link));
        lvm.setAdapter(movieAdapter);
    }

}
class MovieAdapter extends ArrayAdapter{

    private List<MovieModel> movieModelList;
    private int resource;
    private LayoutInflater inflater;
    LinearLayout linear;
    Button btn;

    public MovieAdapter(Context context, int resource, List<MovieModel> objects) {
        super(context, resource, objects);
        movieModelList = objects;
        this.resource = resource;

        inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        if(convertView==null){
            convertView = inflater.inflate(R.layout.row,null);
        }
        TextView txv;


        txv = (TextView)convertView.findViewById(R.id.textView2);
        btn = (Button)convertView.findViewById(R.id.button2);
        linear = (LinearLayout)convertView.findViewById(R.id.linear);

        txv.setText(movieModelList.get(position).getName());
        int id = movieModelList.get(position).getId();

        return convertView;
    }
    public void click(String id){
        btn.setText(id);
    }
}