if String is empty then data is not inserting

INNER JOIN MaritalStatus AS m ON m.MaritalStatusDesc = @maritalStatusDesc

cmd.Parameters.Add(new SqlParameter("@maritalStatusDesc", string.IsNullOrEmpty(MaritalStatusDesc) ? (object)DBNull.Value : MaritalStatusDesc));

WHERE ... AND @maritalStatusDesc Is Not Null

cmd.Parameters.Add(new SqlParameter("@maritalStatusId", IDLookupHelper.GetIDForMaritalStatusDesc(msdTextBox.Text)));

public object GetIDForMaritalStatusDesc(string msd){
  if(string.IsNullOrEmpty(msd))
    return DBNull.Value;
  using(SqlCommand sq = new SqlCommand(
    "connstr here", 
    "SELECT ID FROM MaritalStatusWHERE Desc = @msd"
  );){
    sq.Parameters.AddWithValue("@msd", msd); //note: google "can we stop using addwithvalue already"

    try{ 
      return sq.ExecuteScalar();
    } catch {
      return DBNull.Value
    }
  }
}