Modify map_top_n to throw when nested nulls are present (#11157)

Summary:
Pull Request resolved: #11157

Nested nulls present inhibit the orderbility of values. Currently, any check for nested null is bypassed when 'n' is greater than the size of the map. This chanhe removes the bypass. This will now match Presto's behavior.

Reviewed By: kevinwilfong

Differential Revision: D63796842

fbshipit-source-id: 79ce7b15dea88ff6f7b81d17ed202195c0fdb5f9

velox/functions/prestosql/MapTopN.h

@@ -60,11 +60,6 @@ struct MapTopNFunction {
       return;
     }
 
-    if (n >= inputMap.size()) {
-      out.copy_from(inputMap);
-      return;
-    }
-
     using It = typename arg_type<Map<Orderable<T1>, Orderable<T2>>>::Iterator;
 
     Compare<It> comparator;

velox/functions/prestosql/tests/MapTopNTest.cpp

@@ -66,6 +66,22 @@ TEST_F(MapTopNTest, basic) {
       "n must be greater than or equal to 0");
 }
 
+TEST_F(MapTopNTest, nestedNullFailure) {
+  auto data = makeMapVector(
+      /*offsets=*/{0},
+      /*keyVector=*/makeFlatVector<int32_t>({1, 2, 3}),
+      /*valueVector=*/
+      makeNullableArrayVector<int32_t>({{std::nullopt}, {2}, {5}}));
+
+  // Nested nulls present inhibit the orderbility of values. Expect an error.
+  VELOX_ASSERT_THROW(
+      evaluate("map_top_n(c0, 1)", makeRowVector({data})), // n < map size
+      "Ordering nulls is not supported");
+  VELOX_ASSERT_THROW(
+      evaluate("map_top_n(c0, 10)", makeRowVector({data})), // n > map size
+      "Ordering nulls is not supported");
+}
+
 // Test to ensure we use keys to break ties if values are
 // equal.
 TEST_F(MapTopNTest, equalValues) {