How to solve to invoke virtual method and Sqlite giving NullPointerException in android studio?

Question

I am trying to use SQLite DB to store data along with other information in my android app but i am getting this error:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory, android.database.DatabaseErrorHandler)' on a null object reference.

Here is my ViewProductList.java:

    RecyclerView recyclerView;
    RecyclerView.LayoutManager layoutManager;
    RecyclerAdapter adapter;
    ArrayList<Contact> arrayList = new ArrayList<>();

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

        //DbHelper dbHelper= new DbHelper(this);
        recyclerView = (RecyclerView) findViewById(R.id.recyclerview);
        layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setHasFixedSize(true);

        adapter = new RecyclerAdapter(arrayList);
        recyclerView.setAdapter(adapter);
        readFromLocalStorage();

    }
public void readFromLocalStorage(){
        arrayList.clear();
        DbHelper dbHelper = new DbHelper(this);
        SQLiteDatabase database= dbHelper.getReadableDatabase();

        Cursor cursor = dbHelper.readFromLocalDatabase(database);

        while (cursor.moveToNext()){
            String name=cursor.getString(cursor.getColumnIndex(DbContract.NAME));
            String quantity=cursor.getString(cursor.getColumnIndex(DbContract.QUANTITY));
            String price=cursor.getString(cursor.getColumnIndex(DbContract.PRICE));
            int sync_status =cursor.getInt(cursor.getColumnIndex(DbContract.SYNC_STATUS));

            arrayList.add(new Contact(name,quantity,price,sync_status));
        }
        adapter.notifyDataSetChanged();
        cursor.close();
        dbHelper.close();
    }
}

the error is inside readFromLocalStorage() method please help me to solve it! thank you!

DbHelper.java

public class DbHelper extends SQLiteOpenHelper {

    private static final int DATABASE_VERSION =1;
    private static final String CREATE_TABLE="create table "+DbContract.TABLE_NAME+
            "(id integer primary key autoincrement,"+DbContract.NAME+" text,"+DbContract.QUANTITY+" text,"+DbContract.PRICE+" text,"+DbContract.SYNC_STATUS+
            " integer);";
    private static  final  String DROP_TABLE="drop table if exists "+DbContract.TABLE_NAME;


    public DbHelper(Context context){
        super(context,DbContract.DATABASE_NAME,null,DATABASE_VERSION);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_TABLE);
    }
}

I am getting this error on readFromLocalStorage() method inside ViewProductList.java. Please help me to solve this error. Thankx in advance!