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?
{
            const auto & from_names = from_type->getElementNames();
            std::unordered_map<String, size_t> from_positions;
            from_positions.reserve(from_names.size());
            for (size_t i = 0; i < from_names.size(); ++i)
                from_positions[from_names[i]] = i;
            const auto & to_names = to_type->getElementNames();
            element_wrappers.reserve(to_names.size());
            to_reverse_index.reserve(from_names.size());
            for (size_t i = 0; i < to_names.size(); ++i)
            {
                auto it = from_positions.find(to_names[i]);
                if (it != from_positions.end())
                {
                    element_wrappers.emplace_back(prepareUnpackDictionaries(from_element_types[it->second], to_element_types[i]));
                    to_reverse_index.emplace_back(it->second);
                }
                else
                {
                    element_wrappers.emplace_back();
                    to_reverse_index.emplace_back();
                }
            }
        }
        else
        {
            if (from_element_types.size() != to_element_types.size())
                throw Exception{"CAST AS Tuple can only be performed between tuple types with the same number of elements or from String.\n"
                    "Left type: " + from_type->getName() + ", right type: " + to_type->getName(), ErrorCodes::TYPE_MISMATCH};
            element_wrappers = getElementWrappers(from_element_types, to_element_types);