Why HashMap method returns null object reference?

I've tried to make a HashMap method to get SQLite database data, but when I call the method it returns null reference that made my Android app stop working.

This my code:

HashMap method:

public HashMap<String, String> getUserDetails(){
    HashMap<String,String> user = new HashMap<String,String>();
    String selectQuery = "SELECT  * FROM " + TABLE_LOGIN;

    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(selectQuery, null);

    cursor.moveToFirst();
    if(cursor.getCount() > 0){
        user.put("name", cursor.getString(1));
        user.put("position", cursor.getString(2));
        user.put("level", cursor.getString(3));
        user.put("email", cursor.getString(4));
        user.put("uid", cursor.getString(5));
        user.put("created_at", cursor.getString(6));
    }
    cursor.close();
    db.close();

    return user;
}

and this how I call the method in other class

DatabaseHandler db = new DatabaseHandler(getApplicationContext());
HashMap<String,String> userDetail= db.getUserDetails();
int userLevel = Integer.parseInt(userDetail.get("level").toString());

anyway I use a tutorial reference to make this and merge with my own needs.