private void EncodeIfDefined(DerEncoder DER, string OID, string Value)
        {
            if (Value != null)
            {
                DER.StartSET();
                DER.StartSEQUENCE();
                DER.OBJECT_IDENTIFIER(OID);

                if (DerEncoder.IsPrintable(Value))
                {
                    DER.PRINTABLE_STRING(Value);
                }
                else
                {
                    DER.IA5_STRING(Value);
                }

                DER.EndSEQUENCE();
                DER.EndSET();
            }
        }