[GitHub] [lucene] msokolov commented on a change in pull request #172: LUCENE-9992: write empty vector fields when merging

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

msokolov commented on a change in pull request #172:
URL: https://github.com/apache/lucene/pull/172#discussion_r646529427



##########
File path: lucene/core/src/java/org/apache/lucene/codecs/VectorWriter.java
##########
@@ -104,9 +104,12 @@ private void mergeVectors(FieldInfo mergeFieldInfo, final MergeState mergeState)
         }
       }
     }
-    // Create a new VectorValues by iterating over the sub vectors, mapping the resulting
-    // docids using docMaps in the mergeState.
-    if (subs.size() > 0) {
+    if (subs.size() == 0) {
+      // all segments being merged have no vectors
+      writeField(mergeFieldInfo, VectorValues.EMPTY);
+    } else {
+      // Create a new VectorValues by iterating over the sub vectors, mapping the resulting
+      // docids using docMaps in the mergeState.
       writeField(mergeFieldInfo, new VectorValuesMerger(subs, mergeState));
     }

Review comment:
       Hm, no, it throws an NPE in DocIDMerger.next(); if you create a DocIDMerger with an empty List and then call next(), you get an NPE.




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