PR feedback: Guard against empty query results

Add a check to ensure the transaction list is not empty before calling
getFirst() in getTransaction to prevent a potential NoSuchElementException.

Author: goekay

src/main/java/de/rwth/idsg/steve/service/NotificationServiceForUser.java

@@ -148,6 +148,9 @@ public void ocppTransactionEnded(OcppTransactionEnded event) {
         log.debug("Processing: {}", event);
 
         var transaction = transactionService.getTransaction(event.getParams().getTransactionId());
+        if (transaction == null) {
+            return;
+        }
 
         var user = userService.getUserForMail(transaction.getOcppIdTag(), NotificationFeature.OcppTransactionEnded);
         if (user == null) {

src/main/java/de/rwth/idsg/steve/service/TransactionService.java

@@ -35,6 +35,7 @@
 import org.jetbrains.annotations.Nullable;
 import org.joda.time.DateTime;
 import org.springframework.stereotype.Service;
+import org.springframework.util.CollectionUtils;
 
 import java.io.Writer;
 import java.util.Comparator;
@@ -77,7 +78,11 @@ public Transaction getTransaction(int transactionPk) {
         form.setReturnCSV(false);
         form.setType(TransactionQueryForm.QueryType.ALL);
 
-        return transactionRepository.getTransactions(form).getFirst();
+        List<Transaction> transactions = transactionRepository.getTransactions(form);
+        if (CollectionUtils.isEmpty(transactions)) {
+            return null;
+        }
+        return transactions.getFirst();
     }
 
     public Transaction getLatestActiveTransaction(String chargeBoxId, Integer connectorId) {