Refactored code to remove unnecessary calls to `parse_value`.
Which were affecting filter by enum (rails >= 5.0):
If enum defined like
```
enum size: { L: 'l', S: 's' }
```
Due to multiple calls, the chain when filtering by size is following:
```
parse_value("l") => "L"
parse_value("L") => null
```
Which leads to non working filtering.
NOTE: `parse_value` returns correct result in both cases above

Rails does not support yet pg v1.0.0
more details here: rails/rails#31669