Modified post-trigger last reference checking, to now require a non-null value

This allows for compatibility with TRANSFER_PRIVS validation in commit 8950bb7, which treats any account with a non-null reference as "existing". It also avoids possible unknown side effects from trying to process and store transactions with a null reference - something that wouldn't have been possible until the validation was removed.

src/main/java/org/qortal/transaction/ArbitraryTransaction.java

@@ -90,7 +90,8 @@ public class ArbitraryTransaction extends Transaction {
 
 		// Disable reference checking after feature trigger timestamp
 		if (this.arbitraryTransactionData.getTimestamp() >= BlockChain.getInstance().getDisableReferenceTimestamp()) {
-			return true;
+			// Allow any non-null value
+			return this.arbitraryTransactionData.getReference() != null;
 		}
 
 		if (this.arbitraryTransactionData.getReference() == null) {

src/main/java/org/qortal/transaction/AtTransaction.java

@@ -78,7 +78,8 @@ public class AtTransaction extends Transaction {
 	public boolean hasValidReference() throws DataException {
 		// Disable reference checking after feature trigger timestamp
 		if (this.atTransactionData.getTimestamp() >= BlockChain.getInstance().getDisableReferenceTimestamp()) {
-			return true;
+			// Allow any non-null value
+			return this.atTransactionData.getReference() != null;
 		}
 
 		// Check reference is correct, using AT account, not transaction creator which is null account

src/main/java/org/qortal/transaction/MessageTransaction.java

@@ -167,7 +167,8 @@ public class MessageTransaction extends Transaction {
 
 		// Disable reference checking after feature trigger timestamp
 		if (this.messageTransactionData.getTimestamp() >= BlockChain.getInstance().getDisableReferenceTimestamp()) {
-			return true;
+			// Allow any non-null value
+			return this.messageTransactionData.getReference() != null;
 		}
 
 		if (this.messageTransactionData.getReference() == null)

src/main/java/org/qortal/transaction/Transaction.java

@@ -907,7 +907,8 @@ public abstract class Transaction {
 	public boolean hasValidReference() throws DataException {
 		// Disable reference checking after feature trigger timestamp
 		if (this.transactionData.getTimestamp() >= BlockChain.getInstance().getDisableReferenceTimestamp()) {
-			return true;
+			// Allow any non-null value
+			return this.transactionData.getReference() != null;
 		}
 
 		Account creator = getCreator();

src/test/java/org/qortal/test/TransactionReferenceTests.java

@@ -80,4 +80,30 @@ public class TransactionReferenceTests extends Common {
         }
     }
 
+    @Test
+    public void testNullReferenceAfterFeatureTrigger() throws DataException {
+        Common.useSettings("test-settings-v2-disable-reference.json");
+        Random random = new Random();
+
+        try (final Repository repository = RepositoryManager.getRepository()) {
+            PrivateKeyAccount alice = Common.getTestAccount(repository, "alice");
+
+            byte[] randomPrivateKey = new byte[32];
+            random.nextBytes(randomPrivateKey);
+            PrivateKeyAccount recipient = new PrivateKeyAccount(repository, randomPrivateKey);
+
+            // Create payment transaction data
+            TransactionData paymentTransactionData = new PaymentTransactionData(TestTransaction.generateBase(alice), recipient.getAddress(), 100000L);
+
+            // Set null reference
+            paymentTransactionData.setReference(null);
+
+            Transaction paymentTransaction = Transaction.fromData(repository, paymentTransactionData);
+
+            // Transaction should be invalid, as we require a non-null reference
+            Transaction.ValidationResult validationResult = paymentTransaction.isValidUnconfirmed();
+            assertEquals(Transaction.ValidationResult.INVALID_REFERENCE, validationResult);
+        }
+    }
+
 }