Issue_1427

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

@@ -449,7 +449,10 @@ public class TransactionStore {
                         if (map != null) { // might be null if map was removed later
                             Object key = op[1];
                             commitDecisionMaker.setUndoKey(undoKey);
-                            map.operate(key, null, commitDecisionMaker);
+                            // although second parameter (value) is not really used
+                            // by CommitDecisionMaker, MVRTreeMap has weird traversal logic based on it,
+                            // and any non-null value will do, to signify update, not removal
+                            map.operate(key, VersionedValue.DUMMY, commitDecisionMaker);
                         }
                     }
                     undoLog.clear();