ObjectRenderer doesn't crash when no objects to cache with Rails.cache.read_multi

lib/banzai/renderer.rb

@@ -61,10 +61,16 @@ module Banzai
       end
 
       cacheable_items, non_cacheable_items = items_collection.partition { |item| item.key?(:cache_key) }
-      items_in_cache = Rails.cache.read_multi(*cacheable_items.map { |item| item[:cache_key] })
-      items_not_in_cache = cacheable_items.reject do |item|
-        item[:rendered] = items_in_cache[item[:cache_key]]
-        items_in_cache.key?(item[:cache_key])
+
+      items_in_cache = []
+      items_not_in_cache = []
+
+      unless cacheable_items.empty?
+        items_in_cache = Rails.cache.read_multi(*cacheable_items.map { |item| item[:cache_key] })
+        items_not_in_cache = cacheable_items.reject do |item|
+          item[:rendered] = items_in_cache[item[:cache_key]]
+          items_in_cache.key?(item[:cache_key])
+        end
       end
 
       (items_not_in_cache + non_cacheable_items).each do |item|

spec/lib/banzai/object_renderer_spec.rb

@@ -109,6 +109,17 @@ describe Banzai::ObjectRenderer do
       expect(docs[1]).to be_an_instance_of(Nokogiri::HTML::DocumentFragment)
       expect(docs[1].to_html).to eq('<p>bye</p>')
     end
+
+    it 'returns when no objects to render' do
+      objects = []
+      renderer = described_class.new(project, user, pipeline: :note)
+
+      expect(Banzai).to receive(:cache_collection_render).
+        with([]).
+        and_call_original
+
+      expect(renderer.render_attributes(objects, :note)).to eq([])
+    end
   end
 
   describe '#base_context' do