def get_time_of_tag(tag_name)
      raise ChangelogGeneratorError, "tag_name is nil" if tag_name.nil?

      name_of_tag = tag_name.fetch("name")
      time_for_tag_name = @tag_times_hash[name_of_tag]
      return time_for_tag_name if time_for_tag_name

      @fetcher.fetch_date_of_tag(tag_name).tap do |time_string|
        @tag_times_hash[name_of_tag] = time_string
      end
    end
def get_time_of_tag(tag_name)
      raise ChangelogGeneratorError, "tag_name is nil" if tag_name.nil?

      name_of_tag = tag_name.fetch("name")
      time_for_tag_name = @tag_times_hash[name_of_tag]
      return time_for_tag_name if time_for_tag_name

      @fetcher.fetch_date_of_tag(tag_name).tap do |time_string|
        @tag_times_hash[name_of_tag] = time_string
      end
    end
Returns date for given GitHub Tag hash

 Memoize the date by tag name.

 @param [Hash] tag_name

 @return [Time] time of specified tag