Double aDouble = Optional.ofNullable(wayfairMonthBill.getPaymentAmountDetailJson()) .filter(StringUtils::isNotBlank).map(paymentAmountDetailJson -> JSON .parseArray(paymentAmountDetailJson, WayfairMonthBillPaymentDetailCustom.class)) .map(paymentAmountDetails -> paymentAmountDetails.stream() .map(WayfairMonthBillPaymentDetailCustom::getPaymentAmounts).flatMap(Collection::stream) .mapToDouble(item -> item).sum()).orElse(0.0); return aDouble;