Split polls date range validation

It was a bit strange to leave the end date blank and have a message
associated with the start date, so we're using presence validations
instead.

For the range validation, we're using the comparison validator included
in Rails 7.0.

app/models/poll.rb

@@ -33,7 +33,17 @@ class Poll < ApplicationRecord
   belongs_to :budget
 
   validates_translation :name, presence: true
-  validate :date_range
+
+  validates :starts_at, presence: true
+  validates :ends_at, presence: true
+
+  validates :starts_at,
+            comparison: {
+              less_than_or_equal_to: :ends_at,
+              message: ->(*) { I18n.t("errors.messages.invalid_date_range") }
+            },
+            allow_blank: true,
+            if: -> { ends_at }
   validates :starts_at,
             comparison: {
               greater_than_or_equal_to: ->(*) { Time.current },
@@ -175,12 +185,6 @@ class Poll < ApplicationRecord
     Poll::Voter.where(poll: self, user: user, origin: "web").exists?
   end
 
-  def date_range
-    if starts_at.blank? || ends_at.blank? || starts_at > ends_at
-      errors.add(:starts_at, I18n.t("errors.messages.invalid_date_range"))
-    end
-  end
-
   def start_date_change
     if will_save_change_to_starts_at?
       if starts_at_in_database < Time.current

spec/models/poll/poll_spec.rb

@@ -24,12 +24,14 @@ describe Poll do
       poll.starts_at = nil
 
       expect(poll).not_to be_valid
-      expect(poll.errors[:starts_at]).to eq ["Invalid date range"]
+      expect(poll.errors[:starts_at]).to eq ["can't be blank"]
     end
 
     it "is not valid without an end date" do
       poll.ends_at = nil
+
       expect(poll).not_to be_valid
+      expect(poll.errors[:ends_at]).to eq ["can't be blank"]
     end
 
     it "is not valid without a proper start/end date range" do