fix(joins): Strengthen nullptr check for null aware hash joins with f…

…ilters (facebookincubator#11620)

Summary:

The mayHaveNulls() method sometimes returns true when there are in fact no nulls. This change will make sure that a nullptr isn't passed to memcpy.

Differential Revision: D66333546

velox/exec/HashProbe.cpp

@@ -1212,11 +1212,12 @@ void HashProbe::prepareFilterRowsForNullAwareJoin(
     for (auto& projection : filterInputProjections_) {
       filterInputColumnDecodedVector_.decode(
           *filterInput->childAt(projection.outputChannel), filterInputRows_);
-      if (filterInputColumnDecodedVector_.mayHaveNulls()) {
+      if (const uint64_t* nulls =
+              filterInputColumnDecodedVector_.nulls(&filterInputRows_)) {
         SelectivityVector nullsInActiveRows(numRows);
         memcpy(
             nullsInActiveRows.asMutableRange().bits(),
-            filterInputColumnDecodedVector_.nulls(&filterInputRows_),
+            nulls,
             bits::nbytes(numRows));
         // All rows that are not active count as non-null here.
         bits::orWithNegatedBits(