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?
{
    if constexpr (std::is_same_v<ToDataType, DataTypeDateTime64>)
        return true;
    else if constexpr (std::is_same_v<Name, NameToDateTime> || std::is_same_v<Name, NameParseDateTimeBestEffort>
        || std::is_same_v<Name, NameParseDateTimeBestEffortOrZero> || std::is_same_v<Name, NameParseDateTimeBestEffortOrNull>)
    {
        return (arguments.size() == 2 && isUnsignedInteger(arguments[1].type)) || arguments.size() == 3;
    }
    return false;
}
template <typename ToDataType, typename Name, typename MonotonicityImpl>
class FunctionConvert : public IFunction
{
public:
    using Monotonic = MonotonicityImpl;
    static constexpr auto name = Name::name;
    static constexpr bool to_decimal =
        std::is_same_v<Name, NameToDecimal32> || std::is_same_v<Name, NameToDecimal64>
         || std::is_same_v<Name, NameToDecimal128> || std::is_same_v<Name, NameToDecimal256>;
    static constexpr bool to_datetime64 = std::is_same_v<ToDataType, DataTypeDateTime64>;
    static constexpr bool to_string_or_fixed_string = std::is_same_v<ToDataType, DataTypeFixedString> ||
                                                      std::is_same_v<ToDataType, DataTypeString>;
    static constexpr bool to_date_or_datetime = std::is_same_v<ToDataType, DataTypeDate> ||
                                                std::is_same_v<ToDataType, DataTypeDate32> ||
                                                std::is_same_v<ToDataType, DataTypeDateTime>;
    static FunctionPtr create(ContextPtr) { return std::make_shared<FunctionConvert>(); }