There is an error when you are trying to validate an empty request, like key is missing

<img width="796" alt="Screenshot 2024-01-24 at 14 38 51" src="https://github.com/loqimean/monopay-ruby/assets/49816584/a326495c-490e-42be-9b28-8874f58ab4e8">
 code sample

```ruby
webhook_validator = MonopayRuby::Webhooks::Validator.new(request)

webhook_validator.valid?
```