InvalidOperationException：当不存在数据时尝试读取无效。 （SQL）

      SqlConnection conn = new SqlConnection(AllQuestionsPresented.connectionString);

    SqlCommand cmd = new SqlCommand(sb.ToString(), conn);
    cmd.Parameters.Add(\"@ThreadsID\", SqlDbType.Int).Value = commentIDe;
    cmd.Parameters.Add(\"@CommentsID\", SqlDbType.Int).Value = commentIDe;
    try
    {
        conn.Open();
        SqlDataReader dr = cmd.ExecuteReader(CommandBehavior.CloseConnection);

        if (dr != null && dr[\"Comments\"] != null && dr[\"Name\"] != null && dr[\"Date\"] != null && dr[\"UserID\"]!=null)//> Invalid attempt to read when no data is present.
        {
            Comment = dr[\"Comments\"].ToString();
            UserName = dr[\"Name\"].ToString();
            Reputation=Int32.Parse(dr[\"Reputation\"].ToString());
            Time = (DateTime)AllQuestionsPresented.TryParse(dr[\"Date\"].ToString());
            UserID = (Guid)dr[\"UserID\"];
        }
        dr.Close();
    }
    finally
    {
        if (conn.State != ConnectionState.Closed)
        {
            conn.Close();
        }
    }

                 while (reader.Read())//Command runs through all the ThreadIDs that i have!
                {
                    Comments allQ = new Comments((int)reader[\"CommentsID\"]);
                    allComments.Add(allQ);
                }