cont able to insert the values in to SQLite. got null pointer exception

I was tried to insert some values to my SQLite database. like(id,name,number and image).but i got a null pointer exception while run the code. the values is display in the pojo class while i print using sys out. i dont know what is the problem here. please help me. Thanks in advance.

my code is here

  add.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            picture = data.get(position);
            listModelData.setTitle(String.valueOf(a[position]));
            listModelData.setImageUrl(picture._image);
            listModelData.setitemName(itemname);
            listData.add(listModelData);
            ((MainActivity) context).getData(listData);

        }
    });

   /////////////////////////////////////////////


public class MainActivity extends Activity {
ArrayList<ListModel> listData = new ArrayList<ListModel>();
HorizontalListView listview;
// HorizontalAdapter hAdapter;
HorizantalDBHandler hdb;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    listview = (HorizontalListView) findViewById(R.id.listview);
    // hAdapter = new HorizontalAdapter(getApplicationContext(), listData);
    // listview.setAdapter(hAdapter);

  }

    public void getData(ArrayList<ListModel> listData) {
    // TODO Auto-generated method stub
    System.out.println("@@@@@@@@DDDDDDDDD@@@@@@@@@@");
    int id = 301;
    String value = listData.get(0).getTitle();
    String itemname = listData.get(0).getitemName();
    byte[] image = listData.get(0).getImageUrl();

    System.out.println(value);
    System.out.println(image);
    System.out.println(itemname);
    System.out.println(id);

    hdb.addContact(new HorizantalPojo(id, itemname, value, image));

    System.out.println(value);
    System.out.println(image);
    System.out.println(itemname);
    // hAdapter = new HorizontalAdapter(getApplicationContext(),listData);
    // listview.setAdapter(hAdapter);

    // hAdapter.notifyDataSetChanged();

 }

 }

  ///////////////////////////////////////////////////
public class HorizantalPojo {

// private variables
int _id;
public String _name;
public byte[] _image;
String _number;

// Empty constructor
public HorizantalPojo() {

}


// constructor
public HorizantalPojo(int id, String number, String name, byte[] image) {
    System.out.println("it comessssssssss");
    this._name = name;
    this._image = image;
    this._number = number;
    this._id = id;

    System.out.println(_id);
    System.out.println(_name);
    System.out.println(_image);
    System.out.println(_number);
    System.out.println("it comessssssssss");

 }

// constructor
    public HorizantalPojo(String name, byte[] image) {
    this._name = name;
    this._image = image;
}

// getting ID
public int getID() {
    return this._id;
}

// setting id
public void setID(int keyId) {
    this._id = keyId;
}

// getting name
public String getName() {
    return this._name;
}

// setting name
public void setName(String name) {
    this._name = name;
}

// getting phone number
public byte[] getImage() {
    return this._image;
}

// setting phone number
public void setImage(byte[] image) {
    this._image = image;
}

public String getNumber() {
    return this._number;
}

// setting phone number
public void setNumber(String number) {
    this._number = number;
}

}

/////////////////////////////////////////////////////
public class HorizantalDBHandler extends SQLiteOpenHelper {

// All Static variables
// Database Version
private static final int DATABASE_VERSION = 1;

// Database Name
private static final String DATABASE_NAME = "hrlist";

// Contacts table name
// private static final String TABLE_CONTACTS = "breakfast";
private static final String TABLE_BREAKFAST = "hrlist";

// Contacts Table Columns names

private static final String KEY_ID = "id";
private static final String KEY_NUMBER = "number";
private static final String KEY_NAME = "name";
private static final String KEY_IMAGE = "image";

public HorizantalDBHandler(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

// Creating Tables
@Override
public void onCreate(SQLiteDatabase db) {
    String CREATE_BREAKFAST_TABLE = "CREATE TABLE " + TABLE_BREAKFAST + "("
            + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
            + KEY_NUMBER + " TEXT," + KEY_IMAGE + " BLOB" + ")";

    db.execSQL(CREATE_BREAKFAST_TABLE);
}

// Upgrading database
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // Drop older table if existed
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_BREAKFAST);

    // Create tables again
    onCreate(db);
}

/**
 * All CRUD(Create, Read, Update, Delete) Operations
 */

  public// Adding new contact
  void addContact(HorizantalPojo contact) {
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();

    System.out.println("################");
    System.out.println("################");
    System.out.println("################");
    System.out.println(contact._id);
    System.out.println(contact._name);
    System.out.println(contact._number);
    System.out.println(contact._image);

    values.put(KEY_ID, contact._id);
    values.put(KEY_NAME, contact._name); // Contact Name
    values.put(KEY_NUMBER, contact._number);
    values.put(KEY_IMAGE, contact._image); // Contact Phone
    //
    //
    // Inserting Row
    db.insert(TABLE_BREAKFAST, null, values);
    db.close(); // Closing database connection

}

// // Getting All Contacts
public List<HorizantalPojo> getAllContacts() {
    List<HorizantalPojo> contactList = new ArrayList<HorizantalPojo>();
    // Select All Query
    String selectQuery = "SELECT  * FROM hrlist ORDER BY name";

    SQLiteDatabase db = this.getWritableDatabase();
    Cursor cursor = db.rawQuery(selectQuery, null);
    // looping through all rows and adding to list
    if (cursor.moveToFirst()) {
        do {
            HorizantalPojo contact = new HorizantalPojo();
            contact.setID(Integer.parseInt(cursor.getString(0)));
            contact.setName(cursor.getString(1));
            contact.setImage(cursor.getBlob(2));
            // contact.setNumber(cursor.getString(3));

            System.out.println("^^^^^^^^^^^^^^^^");
            System.out.println("^^^^^^^^^^^^^^^^");
            System.out.println("^^^^^^^^^^^^^^^^");
            System.out.println("^^^^^^^^^^^^^^^^");
            System.out.println(cursor.getString(1));
            System.out.println(cursor.getBlob(2));

            // Adding contact to list
            contactList.add(contact);
        } while (cursor.moveToNext());
    }
    // close inserting data from database
    db.close();
    // return contact list
    return contactList;

}
}