FINERACT-1981: Fix interest refund transaction with zero amount

fineract-loan/src/main/java/org/apache/fineract/portfolio/loanaccount/service/InterestRefundService.java

@@ -18,6 +18,7 @@
  */
 package org.apache.fineract.portfolio.loanaccount.service;
 
+import java.math.MathContext;
 import java.time.LocalDate;
 import java.util.List;
 import org.apache.fineract.organisation.monetary.domain.MonetaryCurrency;
@@ -36,5 +37,5 @@ public interface InterestRefundService {
     Money totalInterestByTransactions(LoanRepaymentScheduleTransactionProcessor processor, Long loanId,
             LocalDate relatedRefundTransactionDate, List<LoanTransaction> newTransactions, List<Long> oldTransactionIds);
 
-    Money getTotalInterestRefunded(List<LoanTransaction> loanTransactions, MonetaryCurrency currency);
+    Money getTotalInterestRefunded(List<LoanTransaction> loanTransactions, MonetaryCurrency currency, MathContext mc);
 }

fineract-provider/src/main/java/org/apache/fineract/portfolio/loanaccount/domain/LoanAccountDomainServiceJpa.java

@@ -18,6 +18,7 @@
  */
 package org.apache.fineract.portfolio.loanaccount.domain;
 
+import jakarta.annotation.Nullable;
 import java.math.BigDecimal;
 import java.time.LocalDate;
 import java.util.ArrayList;
@@ -40,6 +41,7 @@
 import org.apache.fineract.infrastructure.core.exception.PlatformApiDataValidationException;
 import org.apache.fineract.infrastructure.core.service.DateUtils;
 import org.apache.fineract.infrastructure.core.service.ExternalIdFactory;
+import org.apache.fineract.infrastructure.core.service.MathUtil;
 import org.apache.fineract.infrastructure.event.business.domain.loan.LoanBalanceChangedBusinessEvent;
 import org.apache.fineract.infrastructure.event.business.domain.loan.LoanBusinessEvent;
 import org.apache.fineract.infrastructure.event.business.domain.loan.transaction.LoanChargePaymentPostBusinessEvent;
@@ -166,6 +168,7 @@ public void updateLoanCollateralStatus(Set<LoanCollateralManagement> loanCollate
         this.loanCollateralManagementRepository.saveAll(loanCollateralManagementSet);
     }
 
+    @Nullable
     private LoanTransaction createInterestRefundLoanTransaction(Loan loan, LoanTransaction refundTransaction) {
 
         InterestRefundService interestRefundService = interestRefundServiceDelegate.lookupInterestRefundService(loan);
@@ -175,13 +178,17 @@ private LoanTransaction createInterestRefundLoanTransaction(Loan loan, LoanTrans
 
         Money totalInterest = interestRefundService.totalInterestByTransactions(null, loan.getId(), refundTransaction.getTransactionDate(),
                 List.of(), loan.getLoanTransactions().stream().map(AbstractPersistableCustom::getId).toList());
-        Money previouslyRefundedInterests = interestRefundService.getTotalInterestRefunded(loan.getLoanTransactions(), loan.getCurrency());
+        Money previouslyRefundedInterests = interestRefundService.getTotalInterestRefunded(loan.getLoanTransactions(), loan.getCurrency(),
+                totalInterest.getMc());
 
         Money newTotalInterest = interestRefundService.totalInterestByTransactions(null, loan.getId(),
                 refundTransaction.getTransactionDate(), List.of(refundTransaction),
                 loan.getLoanTransactions().stream().map(AbstractPersistableCustom::getId).toList());
         BigDecimal interestRefundAmount = totalInterest.minus(previouslyRefundedInterests).minus(newTotalInterest).getAmount();
 
+        if (MathUtil.isZero(interestRefundAmount)) {
+            return null;
+        }
         final ExternalId txnExternalId = externalIdFactory.create();
         businessEventNotifierService.notifyPreBusinessEvent(new LoanTransactionInterestRefundPreBusinessEvent(loan));
         return LoanTransaction.interestRefund(loan, interestRefundAmount, refundTransaction.getDateOf(), txnExternalId);

fineract-provider/src/main/java/org/apache/fineract/portfolio/loanaccount/service/ProgressiveLoanInterestRefundServiceImpl.java

@@ -21,6 +21,7 @@
 import static org.apache.fineract.portfolio.loanaccount.domain.LoanTransactionType.REPAYMENT;
 
 import java.math.BigDecimal;
+import java.math.MathContext;
 import java.time.LocalDate;
 import java.util.ArrayList;
 import java.util.List;
@@ -135,9 +136,13 @@ public Money totalInterestByTransactions(LoanRepaymentScheduleTransactionProcess
     }
 
     @Override
-    public Money getTotalInterestRefunded(List<LoanTransaction> loanTransactions, MonetaryCurrency currency) {
-        return Money.of(currency, loanTransactions.stream().filter(LoanTransaction::isNotReversed).filter(LoanTransaction::isInterestRefund)
-                .map(LoanTransaction::getAmount).reduce(BigDecimal.ZERO, BigDecimal::add));
+    public Money getTotalInterestRefunded(List<LoanTransaction> loanTransactions, MonetaryCurrency currency, MathContext mc) {
+        final BigDecimal totalInterestRefunded = loanTransactions.stream() //
+                .filter(LoanTransaction::isNotReversed) //
+                .filter(LoanTransaction::isInterestRefund) //
+                .map(LoanTransaction::getAmount) //
+                .reduce(BigDecimal.ZERO, BigDecimal::add); //
+        return Money.of(currency, totalInterestRefunded, mc);
     }
 
 }

integration-tests/src/test/java/org/apache/fineract/integrationtests/LoanInterestRefundTest.java

@@ -1108,6 +1108,35 @@ public void verifyUC18S1() {
         });
     }
 
+    @Test
+    public void verifyNoEmptyInterestRefundTransaction() {
+        runAt("1 January 2021", () -> {
+            PostLoanProductsResponse loanProduct = loanProductHelper
+                    .createLoanProduct(create4IProgressive().daysInMonthType(DaysInMonthType.ACTUAL) //
+                            .daysInYearType(DaysInYearType.ACTUAL) //
+                            .multiDisburseLoan(true)//
+                            .disallowExpectedDisbursements(true)//
+                            .maxTrancheCount(2)//
+                            .addSupportedInterestRefundTypesItem(SupportedInterestRefundTypesItem.PAYOUT_REFUND) //
+                            .addSupportedInterestRefundTypesItem(SupportedInterestRefundTypesItem.MERCHANT_ISSUED_REFUND) //
+                            .recalculationRestFrequencyType(RecalculationRestFrequencyType.DAILY) //
+            );
+            Long loanId = applyAndApproveProgressiveLoan(client.getClientId(), loanProduct.getResourceId(), "1 January 2021", 1000.0, 9.9,
+                    12, null);
+            Assertions.assertNotNull(loanId);
+
+            disburseLoan(loanId, BigDecimal.valueOf(1000), "1 January 2021");
+            loanTransactionHelper.makeLoanRepayment("MerchantIssuedRefund", "1 January 2021", 1000F, loanId.intValue());
+            logLoanTransactions(loanId);
+
+            verifyTransactions(loanId, //
+                    transaction(1000.0, "Disbursement", "01 January 2021"), //
+                    transaction(1000.0, "Merchant Issued Refund", "01 January 2021") //
+            );
+            logLoanTransactions(loanId);
+        });
+    }
+
     @Test
     public void verifyUC18S2() {
         AtomicReference<Long> loanIdRef = new AtomicReference<>();