Custom DAO inheriting from BaseDaoImpl causes NullPointerException

I created my DaoEZTag class that extends BaseDaoImpl which allows to perform operations on the database.

But when I try to call this DAO's class in MyActivity this cause a NullPointerException in

daoTag = DatabaseManager.getInstance().getHelper().getDaoTag();

so in my DatabeHelper, getDaoTag() returns null but I do not understand why ? Thanks yo for your help !

My POJO class

@DatabaseTable(tableName = EZTag.TABLE_NAME, daoClass = EZTag.class)
public class EZTag 
{
public static final String TABLE_NAME = "ez_tag";
public static final String COLUMN_TAG_ID = "tag_id";
public static final String COLUMN_PARENT_TAG_ID = "parent_tag_id";
public static final String COLUMN_TAG_KEYWORD = "keyword";

@DatabaseField(generatedId = true)
private int id;

@DatabaseField(columnName = EZTag.COLUMN_TAG_ID)
private int tagId;

@DatabaseField(columnName = EZTag.COLUMN_PARENT_TAG_ID)
private int parentTagId;

@DatabaseField(columnName = EZTag.COLUMN_TAG_KEYWORD)
private String keyword;

    //Constructor, Getters & Setters

}

MyDatabaseHelper

public class DatabaseHelper extends OrmLiteSqliteOpenHelper {

private static final String TAG = DatabaseHelper.class.getSimpleName();
private DaoEZTag daoTag;

/***************/

public DatabaseHelper(Context context) {
    super(context, Config.Database.NAME, null, Config.Database.VERSION);
}


@Override
public void onCreate(SQLiteDatabase database,ConnectionSource connectionSource) {
    try {
        TableUtils.createTable(connectionSource, EZTag.class);
    } catch (SQLException e) {
        Log.e(TAG, "Can't create database", e);
        throw new RuntimeException(e);
    } catch (java.sql.SQLException e) {
        Log.e(TAG, "Can't create database", e);
    }
}


@Override
public void onUpgrade(SQLiteDatabase db,ConnectionSource connectionSource, int oldVersion, int newVersion) {
    try {
        TableUtils.dropTable(connectionSource, EZTag.class, true);
        onCreate(db, connectionSource);
    } catch (java.sql.SQLException e) {
        Log.e(TAG, "Can't drop databases", e);
    }
}


public DaoEZTag getDaoTag() {
    if (null == daoTag) {
        try {
            daoTag = getDao(EZTag.class);
        }catch (java.sql.SQLException e) {
            e.printStackTrace();
        }
    }
    return daoTag;
}

}

My DatabaseManager

public class DatabaseManager {

static private DatabaseManager instance;

static public void init(Context context) {
    if(null==instance) {
        instance = new DatabaseManager(context);
    }
}

static public DatabaseManager getInstance() {
    return instance;
}

private DatabaseHelper helper;

private DatabaseManager(Context context) {
    helper = new DatabaseHelper(context);
}

public DatabaseHelper getHelper() {
    return helper;
}

}

My custom DAO that extends BaseDaoImpl

public class DaoEZTag extends BaseDaoImpl<EZTag,Integer> 
{
    public DaoEZTag(ConnectionSource connectionSource) throws SQLException {
    super(connectionSource, EZTag.class);
    }

    // Other methods for database operations
}

} And finally my Activity

public class MyActivity extends ActionBarActivity {

private static final String TAG = MyActivity .class.getSimpleName();
private DaoEZTag  daoTag;



@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.my_activity)
    DatabaseManager.init(this);
    daoTag = DatabaseManager.getInstance().getHelper().getDaoTag();
    Log.e(TAG,daoTag.toString());
}
}