Prevented error on nil author from Issuable delegation

app/models/concerns/issuable.rb

@@ -50,6 +50,7 @@ module Issuable
              :email,
              :public_email,
              to: :author,
+             allow_nil: true,
              prefix: true
 
     delegate :name,

spec/models/concerns/issuable_spec.rb

@@ -44,6 +44,34 @@ describe Issue, "Issuable" do
     it { expect(described_class).to respond_to(:assigned) }
   end
 
+  describe 'author_name' do
+    it 'is delegated to author' do
+      expect(issue.author_name).to eq issue.author.name
+    end
+
+    it 'returns nil when author is nil' do
+      issue.author_id = nil
+      issue.save(validate: false)
+
+      expect(issue.author_name).to eq nil
+    end
+  end
+
+  describe 'assignee_name' do
+    it 'is delegated to assignee' do
+      issue.update!(assignee: create(:user))
+
+      expect(issue.assignee_name).to eq issue.assignee.name
+    end
+
+    it 'returns nil when assignee is nil' do
+      issue.assignee_id = nil
+      issue.save(validate: false)
+
+      expect(issue.assignee_name).to eq nil
+    end
+  end
+
   describe "before_save" do
     describe "#update_cache_counts" do
       context "when previous assignee exists" do