https://clickhouse-test-reports.s3.yandex.net/17375/99073c26ee2692f8efe2ab14b2d8ae0fd813b80e/fuzzer/fuzzer.log

```
SELECT
    k,
    topK(v)
FROM 
(
    SELECT
        number % 7 AS k,
        arrayMap(x -> arrayMap(x -> if(x = 0, NULL, toString(x)), range(x)), range(intDiv(number, 1))) AS v
    FROM system.numbers
    LIMIT 257
)
GROUP BY k
ORDER BY k ASC
```
iterator begin()
    {
        if (!buf)
            return end();
        if (this->hasZero())
            return iteratorToZero();
        Cell * ptr = buf;
        auto buf_end = buf + grower.bufSize();
        while (ptr < buf_end && ptr->isZero(*this))
            ++ptr;
        return iterator(this, ptr);
    }
    const_iterator end() const
    {
        
        return const_iterator(this, buf ? buf + grower.bufSize() : buf);
    }
    const_iterator cend() const
    {
        return end();
    }
    iterator end()
    {
        return iterator(this, buf ? buf + grower.bufSize() : buf);
    }
protected:
    const_iterator iteratorTo(const Cell * ptr) const { return const_iterator(this, ptr); }