gistfile1.rb

class NullableDateWriter < Virtus::Attribute::Writer::Coercible
  def coerce(value)
    if value.is_a?(Date)
      value
    elsif value.blank?
      nil
    else
      Date.parse(value)
    end
  end
end

class BookingWizard
  require "nullable_date_writer"

  include Virtus

  extend ActiveModel::Naming
  include ActiveModel::Conversion
  include ActiveModel::Validations
  include ActiveModel::Validations::Callbacks
  
  attribute :date_of_birth, Date, writer_class: NullableDateWriter
end