Activity.java

public class SearchActivity extends AppCompatActivity {

ArrayList<Accordo> chords;
RecyclerView rv;
SearchView sv;
ArrayList<Accordo> filteredList;

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

    /** gestisce la pubblicita */
    MobileAds.initialize(getApplicationContext(), "ca-app-pub-3940256099942544/6300978111");

    AdView searchBanner = (AdView) findViewById(R.id.search_ad);
    AdRequest adRequest = new AdRequest.Builder().build();
    searchBanner.loadAd(adRequest);

    /**-------------------------------*/

    Intent intent = this.getIntent();
    Bundle bundle = intent.getExtras();
    chords = bundle.getParcelableArrayList("chords");
    filteredList = bundle.getParcelableArrayList("chords"); // THIS IS WHAT I DID TO FIX THE CODE

    sv = (SearchView) findViewById(R.id.testo_ricerca);
    sv.setIconifiedByDefault(false);

    rv = (RecyclerView) findViewById(R.id.lista_ricerca);
    rv.setLayoutManager(new LinearLayoutManager(SearchActivity.this, LinearLayoutManager.VERTICAL, false));
    rv.setHasFixedSize(true);

    final SearchAdapter adapter = new SearchAdapter(this, chords);
    rv.setAdapter(adapter);

    //SEARCH
    sv.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
        @Override
        public boolean onQueryTextSubmit(String query) {
            return false;
        }

        @Override
        public boolean onQueryTextChange(String newText) {
            //FILTER AS YOU TYPE
            List<Accordo> filteredModelList = filter(chords, newText);
            adapter.setFilter(filteredModelList);
            return true;
        }
    });

    /** gestisce cosa succede quando un elemento della lista viene cliccato */
    ItemClickSupport.addTo(rv).setOnItemClickListener(new ItemClickSupport.OnItemClickListener(){
        @Override
        public void onItemClicked(RecyclerView recyclerView, int position, View v) {
            Intent intent = new Intent(SearchActivity.this, ChordActivity.class);
            Bundle bundle = new Bundle();
            bundle.putParcelable("selected", filteredList.get(position));
            intent.putExtras(bundle);
            startActivity(intent);
        }
    });

}

private List<Accordo> filter(List<Accordo> models, String query) {
    query = query.toLowerCase();

    filteredList = new ArrayList<>();
    for (Accordo model : models) {
        final String text = model.getName().toLowerCase();
        if (text.contains(query)) {
            filteredList.add(model);
        }
    }
    return filteredList;
}
}