def include?(payment)
      self.find do |included_payment|
        included_payment.installment == ensure_type(PaymentRelease, payment).installment
      end
    end
def include?(payment)
      self.find do |included_payment|
        included_payment.installment == ensure_type(PaymentRelease, payment).installment
      end
    end
Verify if a payment is already included to payment list.
 Returns Boolean.