[Bug](set) fix find null get wrong result on set operators

be/src/vec/common/columns_hashing.h

@@ -152,8 +152,12 @@ struct HashMethodSingleLowNullableColumn : public SingleColumnMethod {
 
     template <typename Data, typename Key>
     ALWAYS_INLINE FindResult find_key_with_hash(Data& data, size_t i, Key key, size_t hash_value) {
-        if (key_column->is_null_at(i) && data.has_null_key_data()) {
-            return FindResult {&data.template get_null_key_data<Mapped>(), true};
+        if (key_column->is_null_at(i)) {
+            if (data.has_null_key_data()) {
+                return FindResult {&data.template get_null_key_data<Mapped>(), true};
+            } else {
+                return FindResult {nullptr, false};
+            }
         }
         return Base::find_key_impl(key, hash_value, data);
     }

regression-test/data/query_p0/operator/test_set_operator.out

@@ -25,3 +25,5 @@
 5	5
 7	7
 
+-- !test --
+

regression-test/suites/query_p0/operator/test_set_operator.groovy

@@ -97,4 +97,31 @@ suite("test_set_operators", "query,p0,arrow_flight_sql") {
     order_qt_select_except """
         select col1, col1 from t1 except select col1, col1 from t2;
     """
+
+    sql """
+        DROP TABLE IF EXISTS a_table;
+    """
+    sql """
+        create table a_table (
+            k1 int null
+        )
+        duplicate key (k1)
+        distributed BY hash(k1) buckets 3
+        properties("replication_num" = "1");
+    """
+    sql """
+        DROP TABLE IF EXISTS b_table;
+    """
+    sql """
+    create table b_table (
+        k1 int null
+    )
+    duplicate key (k1)
+    distributed BY hash(k1) buckets 3
+    properties("replication_num" = "1");
+    """
+
+    sql "insert into a_table select 0;"
+    sql "insert into b_table select null;"
+    qt_test "select * from a_table intersect select * from b_table;"
 }