docs: def _build_params(self):
          ''' método que constrói o dicionario com os parametros que serão usados
          na requisição HTTP Post ao PagSeguro
          
          Returns:
              Um dicionário com os parametros definidos no objeto Payment.
          '''
          params = {}
          params['email'] = self.email
          params['token'] = self.token
          params['currency'] = self.currency
  
          # Atributos opcionais
          if self.receiver_email:
              params['receiver_email'] = self.receiver_email
          if self.reference:
              params['reference'] = self.reference
          if self.extra_amount:
              params['extra_amount'] = self.extra_amount
          if self.redirect_url:
              params['redirect_url'] = self.redirect_url
          if self.notification_url:
              params['notification_url'] = self.notification_url
          if self.max_uses:
              params['max_uses'] = self.max_uses
          if self.max_age:
              params['max_age'] = self.max_age
  
          #TODO: Incluir metadata aqui
  
          # Itens
          for index, item in enumerate(self.items, start=1):
              params['itemId%d' % index] = item['item_id']
              params['itemDescription%d' % index] = item['description']
              params['itemAmount%d' % index] = '%.2f' % item['amount']
              params['itemQuantity%s' % index] = item['quantity']
              if item.get('shipping_cost'):
                  params['itemShippingCost%d' % index] = item['shipping_cost']
              if item.get('weight'):
                  params['itemWeight%d' % index] = item['weight']
  
          # Sender
          if self.client.get('email'):
              params['senderEmail'] = self.client.get('email')
          if self.client.get('name'):
              params['senderName'] = ' '.join(self.client.get('name').split())
          if self.client.get('phone_area_code'):
              params['senderAreaCode'] = self.client.get('phone_area_code')
          if self.client.get('phone_number'):
              params['senderPhone'] = self.client.get('phone_number')
          if self.client.get('cpf'):
              params['senderCPF'] = self.client.get('cpf')
          if self.client.get('sender_born_date'):
              params['senderBornDate'] = self.client.get('sender_born_date')
  
          # Shipping
          if self.shipping.get('type'):
              params['shippingType'] = self.shipping.get('type')
          if self.shipping.get('cost'):
              params['shippingCost'] = '%.2f' % self.shipping.get('cost')
          if self.shipping.get('country'):
              params['shippingAddressCountry'] = self.shipping.get('country')
          if self.shipping.get('state'):
              params['shippingAddressState'] = self.shipping.get('state')
          if self.shipping.get('city'):
              params['shippingAddressCity'] = self.shipping.get('city')
          if self.shipping.get('postal_code'):
              params['shippingAddressPostalCode'] = self.shipping.get('postal_code')
          if self.shipping.get('district'):
              params['shippingAddressDistrict'] = self.shipping.get('district')
          if self.shipping.get('street'):
              params['shippingAddressStreet'] = self.shipping.get('street')
          if self.shipping.get('number'):
              params['shippingAddressNumber'] = self.shipping.get('number')
          if self.shipping.get('complement'):
              params['shippingAddressComplement'] = self.shipping.get('complement')
  
          return params