replace faulty assertion

h2/src/main/org/h2/mvstore/tx/RollbackDecisionMaker.java

@@ -30,19 +30,22 @@ final class RollbackDecisionMaker extends MVMap.DecisionMaker<Object[]> {
     @Override
     public MVMap.Decision decide(Object[] existingValue, Object[] providedValue) {
         assert decision == null;
-        assert existingValue != null;
-        VersionedValue valueToRestore = (VersionedValue) existingValue[2];
-        long operationId;
-        if (valueToRestore == null ||
-                (operationId = valueToRestore.getOperationId()) == 0 ||
-                TransactionStore.getTransactionId(operationId) == transactionId
-                        && TransactionStore.getLogId(operationId) < toLogId) {
-            int mapId = (Integer) existingValue[0];
-            MVMap<Object, VersionedValue> map = store.openMap(mapId);
-            if (map != null && !map.isClosed()) {
-                Object key = existingValue[1];
-                VersionedValue previousValue = map.operate(key, valueToRestore, MVMap.DecisionMaker.DEFAULT);
-                listener.onRollback(map, key, previousValue, valueToRestore);
+        // normaly existingValue will always be there except of db initialization
+        // where some undo log enty was captured on disk but actual map entry was not
+        if (existingValue != null ) {
+            VersionedValue valueToRestore = (VersionedValue) existingValue[2];
+            long operationId;
+            if (valueToRestore == null ||
+                    (operationId = valueToRestore.getOperationId()) == 0 ||
+                    TransactionStore.getTransactionId(operationId) == transactionId
+                            && TransactionStore.getLogId(operationId) < toLogId) {
+                int mapId = (Integer) existingValue[0];
+                MVMap<Object, VersionedValue> map = store.openMap(mapId);
+                if (map != null && !map.isClosed()) {
+                    Object key = existingValue[1];
+                    VersionedValue previousValue = map.operate(key, valueToRestore, MVMap.DecisionMaker.DEFAULT);
+                    listener.onRollback(map, key, previousValue, valueToRestore);
+                }
             }
         }
         decision = MVMap.Decision.REMOVE;