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 (const auto * from_tuple = checkAndGetDataType<DataTypeTuple>(from_type_untyped.get()))
        {
            if (from_tuple->getElements().size() != 2)
                throw Exception{"CAST AS Map from tuple requeires 2 elements.\n"
                    "Left type: " + from_tuple->getName() + ", right type: " + to_type->getName(), ErrorCodes::TYPE_MISMATCH};
            DataTypes from_kv_types;
            const auto & to_kv_types = to_type->getKeyValueTypes();
            for (const auto & elem : from_tuple->getElements())
            {
                const auto * type_array = checkAndGetDataType<DataTypeArray>(elem.get());
                if (!type_array)
                    throw Exception(ErrorCodes::TYPE_MISMATCH,
                        "CAST AS Map can only be performed from tuples of array. Got: {}", from_tuple->getName());
                from_kv_types.push_back(type_array->getNestedType());