[GitHub] [druid] jihoonson commented on a change in pull request #11890: HashJoinEngine: Fix extraneous advance of left cursor.

[GitBox <gi...@apache.org>]

jihoonson commented on a change in pull request #11890:
URL: https://github.com/apache/druid/pull/11890#discussion_r745947647



##########
File path: processing/src/main/java/org/apache/druid/segment/RowWalker.java
##########
@@ -60,13 +61,16 @@ public T currentRow()
 
   public void advance()
   {
-    if (rowIterator.hasNext()) {
+    if (rowIterator == null) {
+      throw new IllegalStateException("cannot call advance when isDone == true");
+    } else if (rowIterator.hasNext()) {
       current = rowIterator.next();
 
       if (current == null) {
         throw new NullPointerException("null row encountered in walker");
       }
     } else {
+      rowIterator = null;

Review comment:
       nit: perhaps better do `assert rowIterator == null` in `isDone()`.




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