21.7.3 throws an exception if `_sample_factor` is used in a query:
```
CREATE TABLE sessions
(
  `user_id` UInt64
)
ENGINE = MergeTree
ORDER BY user_id 
SAMPLE BY user_id;

insert into sessions values(1);

SELECT
    sum(user_id * _sample_factor) 
FROM sessions
SAMPLE 10000000

DB::Exception: Cannot find column `user_id` in source stream (version 21.8.1.7409 (official build))

SELECT
    sum(user_id) 
FROM sessions
SAMPLE 10000000

sum(user_id)
------------
           1
```
No exception on 21.6.5
if (stat.type == IndexType::None)
                continue;
            auto index_map = std::make_unique<JSONBuilder::JSONMap>();
            index_map->add("Type", indexTypeToString(stat.type));
            if (!stat.name.empty())
                index_map->add("Name", stat.name);
            if (!stat.description.empty())
                index_map->add("Description", stat.description);
            if (!stat.used_keys.empty())
            {
                auto keys_array = std::make_unique<JSONBuilder::JSONArray>();
                for (const auto & used_key : stat.used_keys)
                    keys_array->add(used_key);
                index_map->add("Keys", std::move(keys_array));
            }
            if (!stat.condition.empty())
                index_map->add("Condition", stat.condition);
            if (i)
                index_map->add("Initial Parts", index_stats[i - 1].num_parts_after);
            index_map->add("Selected Parts", stat.num_parts_after);
            if (i)
                index_map->add("Initial Granules", index_stats[i - 1].num_granules_after);
            index_map->add("Selected Granules", stat.num_granules_after);
            indexes_array->add(std::move(index_map));
        }
        map.add("Indexes", std::move(indexes_array));
    }
}
}