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?
src_converted_to_full_column = !removeNullable(arg.type)->equals(*removeNullable(res_type));
                    if (src_converted_to_full_column)
                        arg.column = arg.column->index(col_low_cardinality->getIndexes(), 0);
                    else
                        res_indexes = col_low_cardinality->getIndexesPtr();
                    tmp_rows_count = arg.column->size();
                }
                
                converted_column = wrapper(args, res_type, nullable_source, tmp_rows_count);
            }
            if (to_low_cardinality)
            {
                auto res_column = to_low_cardinality->createColumn();
                auto * col_low_cardinality = typeid_cast<ColumnLowCardinality *>(res_column.get());
                if (from_low_cardinality && !src_converted_to_full_column)
                {
                    col_low_cardinality->insertRangeFromDictionaryEncodedColumn(*converted_column, *res_indexes);
                }
                else
                    col_low_cardinality->insertRangeFromFullColumn(*converted_column, 0, converted_column->size());
                return res_column;
            }
            else if (!src_converted_to_full_column)
                return converted_column->index(*res_indexes, 0);
            else
                return converted_column;
        };
    }
    WrapperType prepareRemoveNullable(const DataTypePtr & from_type, const DataTypePtr & to_type, bool skip_not_null_check) const