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?
{
public:
    static constexpr auto name = Name::name;
    static constexpr bool to_decimal =
        std::is_same_v<ToDataType, DataTypeDecimal<Decimal32>> ||
        std::is_same_v<ToDataType, DataTypeDecimal<Decimal64>> ||
        std::is_same_v<ToDataType, DataTypeDecimal<Decimal128>> ||
        std::is_same_v<ToDataType, DataTypeDecimal<Decimal256>>;
    static constexpr bool to_datetime64 = std::is_same_v<ToDataType, DataTypeDateTime64>;
    static FunctionPtr create(ContextPtr) { return std::make_shared<FunctionConvertFromString>(); }