android SQLiteDatabase query method crashes

My method getHomework should read a row from table, create object Homework, fill the object with data and return it.

my code:

public Homework getHomework(long id){ 

    SQLiteDatabase db = this.getReadableDatabase(); 

    String[] selectionArgs = { String.valueOf(id) };
    Cursor cursor = db.query(TABLE_HOMEWORK, COLUMNS, KEY_ID + "= ?", selectionArgs, null, null, KEY_ID + " DESC");

    Homework homework = new Homework();
    homework.setId(Long.parseLong(cursor.getString(0)));
    homework.setDate(cursor.getString(1));
    homework.setNotification_time(cursor.getString(2));
    homework.setSubject(cursor.getString(3));
    homework.setContent(cursor.getString(4));
    homework.setDescription(cursor.getString(5));


    db.close();

    // 5. return homework
    return homework;
}

But my app always crashes in the line Cursor cursor... I also tried rawQuery(query, null) method instead of query method, but it didn't help.