#vulnerable code 
                                @Override
    public ExchangeRate getExchangeRate(ConversionQuery conversionQuery) {
        if (!isAvailable(conversionQuery)) {
            return null;
        }
        CurrencyUnit base = conversionQuery.getBaseCurrency();
        CurrencyUnit term = conversionQuery.getCurrency();
        LocalDate timestamp = conversionQuery.get(LocalDate.class);
        if (timestamp == null) {
            LocalDateTime dateTime = conversionQuery.get(LocalDateTime.class);
            if (dateTime != null) {
                timestamp = dateTime.toLocalDate();
            }
        }
        ExchangeRate rate1 = lookupRate(currencyToSdr.get(base), timestamp);
        ExchangeRate rate2 = lookupRate(sdrToCurrency.get(term), timestamp);
        if (base.equals(SDR)) {
            return rate2;
        } else if (term.equals(SDR)) {
            return rate1;
        }
        if (Objects.isNull(rate1) || Objects.isNull(rate2)) {
            return null;
        }
        ExchangeRateBuilder builder =
                new ExchangeRateBuilder(ConversionContext.of(CONTEXT.getProviderName(), RateType.HISTORIC));
        builder.setBase(base);
        builder.setTerm(term);
        builder.setFactor(multiply(rate1.getFactor(), rate2.getFactor()));
        builder.setRateChain(rate1, rate2);
        return builder.build();
    } 
                            #location 29 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public ExchangeRate getExchangeRate(ConversionQuery conversionQuery) {
        if (!isAvailable(conversionQuery)) {
            return null;
        }
        CurrencyUnit base = conversionQuery.getBaseCurrency();
        CurrencyUnit term = conversionQuery.getCurrency();
        LocalDate timestamp = getTimeStamp(conversionQuery);
        ExchangeRate rate1 = lookupRate(currencyToSdr.get(base), timestamp);
        ExchangeRate rate2 = lookupRate(sdrToCurrency.get(term), timestamp);
        if (base.equals(SDR)) {
            return rate2;
        } else if (term.equals(SDR)) {
            return rate1;
        }
        if (Objects.isNull(rate1) || Objects.isNull(rate2)) {
            return null;
        }
        ExchangeRateBuilder builder =
                new ExchangeRateBuilder(ConversionContext.of(CONTEXT.getProviderName(), RateType.HISTORIC));
        builder.setBase(base);
        builder.setTerm(term);
        builder.setFactor(multiply(rate1.getFactor(), rate2.getFactor()));
        builder.setRateChain(rate1, rate2);
        return builder.build();
    }