Handle missing parent when deleting comment

When a post is deleted, a comment retraction might race with a post retraction,
causing the comment deletion to raise because of a missing parent

app/models/comment.rb

@@ -47,8 +47,8 @@ class Comment < ApplicationRecord
   end
 
   after_destroy do
-    self.parent.update_comments_counter
-    participation = author.participations.find_by(target_id: post.id)
+    parent.update_comments_counter if parent
+    participation = author.participations.find_by(target_id: commentable_id)
     participation.unparticipate! if participation.present?
   end
 

spec/models/comment_spec.rb

@@ -24,6 +24,14 @@
       participations = Participation.where(target_id: comment_alice.commentable_id, author_id: comment_alice.author_id)
       expect(participations.first.count).to eq(1)
     end
+
+    it "should work if parent is gone" do
+      comment_alice.parent.delete
+      comment_alice.reload
+      expect {
+        comment_alice.destroy
+      }.to_not raise_error
+    end
   end
 
   describe "#subscribers" do