**How to reproduce**
Clickhouse version 20.11.5.18, 20.8.7.15, 20.3.19
```
SELECT
    groupUniqArray(val) AS uniq,
    toTypeName(uniq),
    groupArray(val) AS arr,
    toTypeName(arr)
FROM
(
    SELECT CAST(number % 2, 'Enum(\'hello\' = 1, \'world\' = 0)') AS val
    FROM numbers(2)
)

Query id: d4657f27-c8bd-4174-9947-c6c48d0222d5

┌─uniq──┬─toTypeName(groupUniqArray(val))─┬─arr───────────────┬─toTypeName(groupArray(val))────────────┐
│ [0,1] │ Array(Int8)                     │ ['world','hello'] │ Array(Enum8('world' = 0, 'hello' = 1)) │
└───────┴─────────────────────────────────┴───────────────────┴────────────────────────────────────────┘
```

{
        [[maybe_unused]] auto a = new (place) Data;
        if constexpr (Trait::sampler == Sampler::RNG)
            a->rng.seed(seed);
    }
    void add(AggregateDataPtr place, const IColumn ** columns, size_t row_num, Arena * arena) const override
    {
        if constexpr (Trait::sampler == Sampler::NONE)
        {
            if (limit_num_elems && this->data(place).value.size() >= max_elems)
                return;
            this->data(place).value.push_back(assert_cast<const ColumnVector<T> &>(*columns[0]).getData()[row_num], arena);
        }
        if constexpr (Trait::sampler == Sampler::RNG)
        {
            auto & a = this->data(place);
            ++a.total_values;
            if (a.value.size() < max_elems)
                a.value.push_back(assert_cast<const ColumnVector<T> &>(*columns[0]).getData()[row_num], arena);
            else
            {
                UInt64 rnd = a.genRandom(a.total_values);
                if (rnd < max_elems)
                    a.value[rnd] = assert_cast<const ColumnVector<T> &>(*columns[0]).getData()[row_num];
            }
        }
        
        
    }
    void merge(AggregateDataPtr place, ConstAggregateDataPtr rhs, Arena * arena) const override