Skip { after: :other_attribute } validation if other_attribute is nil

[slucaskim]

🦄 Feature Request

Is your feature request related to a problem?

When I'm using the after syntax using an attribute:

validates :expiration_date, date: { after: :packaging_date }

but then packaging_date is a nilable attribute, the validation fails when packaging_date is blank.

Describe the solution you'd like

The more sensible behaviour to me is if the after validation is only applied in case where packaging_date is present. If packaging_date is blank, the date validation should just check the date format of expiration_date.
If this makes sense with the authors and the users, I'm totally willing to put in a PR!

[Ceda]

next if option_value.blank? to > https://github.com/codegram/date_validator/blob/master/lib/active_model/validations/date_validator.rb#L84