updating credit amount functionality

src/main/java/zw/qantra/tm/domain/services/TransactionService.java

@@ -35,6 +35,10 @@ public class TransactionService {
     private final CurrencyService currencyService;
 
     public BigDecimal calculateCurrencyExchangeValue(CurrencyType from, CurrencyType to, BigDecimal amount) {
+        if (to == null) {
+            return BigDecimal.ZERO;
+        }
+
         Currency debitCurrency = currencyService.findCurrencyByIsoCode(from.name());
         Currency creditCurrency = currencyService.findCurrencyByIsoCode(to.name());