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());
 

src/test/java/zw/qantra/tm/domain/services/TransactionServiceTest.java

@@ -130,10 +130,12 @@ class TransactionServiceTest {
         when(currencyService.findCurrencyByIsoCode("USD")).thenReturn(currencyUsd);
         when(currencyService.findCurrencyByIsoCode("ZWL")).thenReturn(currencyZwl);
 
-        BigDecimal creditAmount = transactionService.calculateCurrencyExchangeValue(transaction);
+        BigDecimal creditAmount = transactionService.calculateCurrencyExchangeValue(
+                transaction.getDebitCurrency(),
+                transaction.getCreditCurrency(),
+                transaction.getAmount());
 
         assertEquals(new BigDecimal("1500.0000"), creditAmount);
-        assertEquals(new BigDecimal("1500.0000"), transaction.getCreditAmount());
     }
 
     @Test
@@ -141,7 +143,10 @@ class TransactionServiceTest {
     void shouldReturnZeroWhenCreditCurrencyNull() {
         transaction.setCreditCurrency(null);
 
-        BigDecimal result = transactionService.calculateCurrencyExchangeValue(transaction);
+        BigDecimal result = transactionService.calculateCurrencyExchangeValue(
+                transaction.getDebitCurrency(),
+                transaction.getCreditCurrency(),
+                transaction.getAmount());
 
         assertEquals(BigDecimal.ZERO, result);
     }