I expect it should work:
```
:) select CAST(CAST('{"x" : 1}', 'Object(\'json\')'), 'Object(Nullable(\'json\'))')

SELECT CAST(CAST('{"x" : 1}', 'Object(\'json\')'), 'Object(Nullable(\'json\'))')

Query id: fb057b45-b72a-4d22-9b38-a3136cdf2465


0 rows in set. Elapsed: 0.002 sec.

Received exception from server (version 22.5.1):
Code: 53. DB::Exception: Received from localhost:9000. DB::Exception: Cast to Object can be performed only from flatten named Tuple, Map or String. Got: Object('json'): While processing CAST(CAST('{"x" : 1}', 'Object(\'json\')'), 'Object(Nullable(\'json\'))'). (TYPE_MISMATCH)
```

@CurtizJ what do you think?
throw Exception("Illegal column " + col_from->getName()
                + " of first argument of function " + Name::name,
                ErrorCodes::ILLEGAL_COLUMN);
        size_t size = input_rows_count;
        typename ColVecTo::MutablePtr col_to = nullptr;
        if constexpr (IsDataTypeDecimal<ToDataType>)
        {
            UInt32 scale = additions;
            if constexpr (to_datetime64)
            {
                ToDataType check_bounds_in_ctor(scale, local_time_zone ? local_time_zone->getTimeZone() : String{});
            }
            else
            {
                ToDataType check_bounds_in_ctor(ToDataType::maxPrecision(), scale);
            }
            col_to = ColVecTo::create(size, scale);
        }
        else
            col_to = ColVecTo::create(size);
        typename ColVecTo::Container & vec_to = col_to->getData();
        ColumnUInt8::MutablePtr col_null_map_to;
        ColumnUInt8::Container * vec_null_map_to [[maybe_unused]] = nullptr;
        if constexpr (exception_mode == ConvertFromStringExceptionMode::Null)
        {
            col_null_map_to = ColumnUInt8::create(size);
            vec_null_map_to = &col_null_map_to->getData();
        }
        const ColumnString::Chars * chars = nullptr;
        const IColumn::Offsets * offsets = nullptr;