code: @Override
      public float getUnitCost(String CorpNum, MessageType MsgType)
              throws PopbillException {
          if (MsgType == null)
              throw new PopbillException(-99999999, "메시지 유형이 입력되지 않았습니다.");
  
          UnitCostResponse response = httpget(
                  "/Message/UnitCost?Type=" + MsgType.name(), CorpNum, null,
                  UnitCostResponse.class);
  
          return response.unitCost;
      }
docs: /*
  (non-Javadoc)
  @see com.popbill.api.MessageService#getUnitCost(java.lang.String, com.popbill.api.message.MessageType)