Adding test for non-existing key on Dry::Validations::Value#[]
Adding test for non-existing key on Dry::Validations::Value#[]

The current behavior is returning nil when requesting a
non-existing key. Changing to use `fetch_values` should
not change that behavior

dryrb/dry-validation,dry-rb/dry-validation,dryrb/dry-validator,dry-rb/dry-validation