CE port for milestones should not be set on epics issue promotion

app/models/concerns/issuable.rb

@@ -427,4 +427,11 @@ module Issuable
   def wipless_title_changed(old_title)
     old_title != title
   end
+
+  ##
+  # Overridden on EE module
+  #
+  def supports_milestone?
+    respond_to?(:milestone_id)
+  end
 end

app/services/issuable/clone/attributes_rewriter.rb

@@ -17,6 +17,8 @@ module Issuable
       private
 
       def cloneable_milestone
+        return unless new_entity.supports_milestone?
+
         title = original_entity.milestone&.title
         return unless title
 

spec/models/concerns/issuable_spec.rb

@@ -774,4 +774,25 @@ describe Issuable do
       end
     end
   end
+
+  describe '#supports_milestone?' do
+    let(:group)   { create(:group) }
+    let(:project) { create(:project, group: group) }
+
+    context "for issues" do
+      let(:issue) { build(:issue, project: project) }
+
+      it 'returns true' do
+        expect(issue.supports_milestone?).to be_truthy
+      end
+    end
+
+    context "for merge requests" do
+      let(:merge_request) { build(:merge_request, target_project: project, source_project: project) }
+
+      it 'returns true' do
+        expect(merge_request.supports_milestone?).to be_truthy
+      end
+    end
+  end
 end