adding NotImplementedError when trying to include polymorphic relationships

lib/fast_jsonapi/object_serializer.rb

@@ -237,7 +237,7 @@ module FastJsonapi
           parse_include_item(include_item).each do |parsed_include|
             relationship_to_include = klass.relationships_to_serialize[parsed_include]
             raise ArgumentError, "#{parsed_include} is not specified as a relationship on #{klass.name}" unless relationship_to_include
-
+            raise NotImplementedError if relationship_to_include[:polymorphic].is_a?(Hash)
             klass = relationship_to_include[:serializer].to_s.constantize
           end
         end

lib/fast_jsonapi/serialization_core.rb

@@ -134,7 +134,7 @@ module FastJsonapi
           items = parse_include_item(include_item)
           items.each do |item|
             next unless relationships_to_serialize && relationships_to_serialize[item]
-
+            raise NotImplementedError if @relationships_to_serialize[item][:polymorphic].is_a?(Hash)
             record_type = @relationships_to_serialize[item][:record_type]
             serializer = @relationships_to_serialize[item][:serializer].to_s.constantize
             relationship_type = @relationships_to_serialize[item][:relationship_type]

spec/lib/object_serializer_spec.rb

@@ -199,10 +199,10 @@ describe FastJsonapi::ObjectSerializer do
         expect(advertising_campaigns_serialized).to include(advertising_campaign.id)
       end
     end
-    it 'polymorphic' do
+    it 'polymorphic throws an error that polymorphic is not supported' do
       options = {}
       options[:include] = [:groupees]
-      serializable_hash = GroupSerializer.new([group], options).serializable_hash
+      expect(-> { GroupSerializer.new([group], options)}).to raise_error(NotImplementedError)
     end
   end