Nacitani z SQL s null parametrem

public List<ZemreliModel> VyhledatZemrele(string jmeno, string prijmeni, bool? peklo, int? rc)
        {
            List<ZemreliModel> temp = new List<ZemreliModel>();
            commandText = "Select * from Zemreli WHERE @jmeno IS NULL OR jmeno = @jmeno";

            using (SqlCeConnection conn = base.NewConnection())
            {
                conn.Open();
                myCommand = new SqlCeCommand(commandText, conn);
                if (jmeno == string.Empty)
                {
                    myCommand.Parameters.AddWithValue("@jmeno", DBNull.Value);
                }
                else
                {
                    myCommand.Parameters.AddWithValue("@jmeno", jmeno);
                }

                SqlCeDataReader myReader = null;
                myReader = myCommand.ExecuteReader();
                temp.Clear();
                while (myReader.Read())
                {
                    if (myReader[4].ToString() == "1")
                    {
                        temp.Add(new ZemreliModel(Int32.Parse(myReader[0].ToString()), myReader[1].ToString(), myReader[2].ToString(), myReader[3].ToString(), true, Int32.Parse(myReader[5].ToString())));
                    }
                    else
                    {
                        temp.Add(new ZemreliModel(Int32.Parse(myReader[0].ToString()), myReader[1].ToString(), myReader[2].ToString(), myReader[3].ToString(), false, Int32.Parse(myReader[5].ToString())));
                    }
                }
                myReader.Close();
                conn.Close();
            }
            return temp;
        }