**Describe what's wrong**

```sql
SELECT toTypeName(s), toString(s) FROM
(
 SELECT toFixedString('',32) AS s 
 UNION ALL
 SELECT null AS s 
)
```

this query works in all versions from 19.17 to 21.8, but stop works after 21.9+ 

https://fiddle.clickhouse.com/7bd65b36-a6e6-470a-8bdc-4c98a33ff453
21.8 works

https://fiddle.clickhouse.com/9e40a424-4027-4c7f-bd41-b20935ae9129
21.9 doesn't work
```
Received exception from server (version 21.9.6):
Code: 44. DB::Exception: Received from localhost:9000. DB::Exception: Illegal column Nullable(FixedString(32)) of first argument of function toString. (ILLEGAL_COLUMN)
```

this query works in all versions

```sql
SELECT toTypeName(s), toString(s) FROM
(
 SELECT '' AS s 
 UNION ALL
 SELECT null AS s 
)
```
https://fiddle.clickhouse.com/4f810f03-1644-4eb7-b696-0341b1bbdbc4


**Does it reproduce on recent release?**
Yes, reproduce in all releases 21.9+
return DecimalUtils::decimalFromComponentsWithMultiplier<DateTime64>(from, 0, scale_multiplier);
    }
};
template <typename FromDataType, typename FromType>
struct ToDateTime64TransformFloat
{
    static constexpr auto name = "toDateTime64";
    const UInt32 scale = 1;
    ToDateTime64TransformFloat(UInt32 scale_ = 0) 
        : scale(scale_)
    {}
    inline NO_SANITIZE_UNDEFINED DateTime64::NativeType execute(FromType from, const DateLUTImpl &) const
    {
        if (from < 0)
            return 0;
        from = std::min<FromType>(from, FromType(0xFFFFFFFF));
        return convertToDecimal<FromDataType, DataTypeDateTime64>(from, scale);
    }
};
template <typename Name> struct ConvertImpl<DataTypeInt8, DataTypeDateTime64, Name>
    : DateTimeTransformImpl<DataTypeInt8, DataTypeDateTime64, ToDateTime64TransformSigned<Int8>> {};
template <typename Name> struct ConvertImpl<DataTypeInt16, DataTypeDateTime64, Name>
    : DateTimeTransformImpl<DataTypeInt16, DataTypeDateTime64, ToDateTime64TransformSigned<Int16>> {};
template <typename Name> struct ConvertImpl<DataTypeInt32, DataTypeDateTime64, Name>
    : DateTimeTransformImpl<DataTypeInt32, DataTypeDateTime64, ToDateTime64TransformSigned<Int32>> {};
template <typename Name> struct ConvertImpl<DataTypeInt64, DataTypeDateTime64, Name>
    : DateTimeTransformImpl<DataTypeInt64, DataTypeDateTime64, ToDateTime64TransformSigned<Int64>> {};
template <typename Name> struct ConvertImpl<DataTypeUInt64, DataTypeDateTime64, Name>
    : DateTimeTransformImpl<DataTypeUInt64, DataTypeDateTime64, ToDateTime64TransformUnsigned<UInt64>> {};
template <typename Name> struct ConvertImpl<DataTypeFloat32, DataTypeDateTime64, Name>