Question: user association is optional

app/models/question.rb

@@ -1,7 +1,7 @@
 class Question < ApplicationRecord
   include Question::AnswerMethods
 
-  belongs_to :user
+  belongs_to :user, optional: true
   has_many :answers, dependent: :destroy
   has_many :inboxes, dependent: :destroy
 

spec/controllers/ajax/answer_controller_spec.rb

@@ -186,7 +186,7 @@ describe Ajax::AnswerController, type: :controller do
 
   describe "#destroy" do
     let(:answer_user) { user }
-    let(:question) { FactoryBot.create(:question, user: FactoryBot.create(:user)) }
+    let(:question) { FactoryBot.create(:question) }
     let(:answer) { FactoryBot.create(:answer, user: answer_user, question: question) }
     let(:answer_id) { answer.id }