[FIX] Fetch json key from item serializer if empty collection is passed to collection serializer and each_searializer is specified.

test/collection_serializer_test.rb

@@ -84,6 +84,12 @@ module ActiveModel
         assert_nil serializer.json_key
       end
 
+      def test_json_key_with_empty_resources_with_serializer
+        resource = []
+        serializer = collection_serializer.new(resource, serializer: MessagesSerializer)
+        assert_equal 'messages', serializer.json_key
+      end
+
       def test_json_key_with_root
         expected = 'custom_root'
         serializer = collection_serializer.new(@resource, root: expected)

test/fixtures/poro.rb

@@ -183,6 +183,12 @@ PaginatedSerializer = Class.new(ActiveModel::Serializer::CollectionSerializer) d
   end
 end
 
+MessagesSerializer = Class.new(ActiveModel::Serializer) do
+  def json_key
+    'messages'
+  end
+end
+
 AlternateBlogSerializer = Class.new(ActiveModel::Serializer) do
   attribute :id
   attribute :name, key: :title