In case of Etag cache hit, the body should be empty

lib/gitlab/etag_caching/middleware.rb

@@ -69,7 +69,7 @@ module Gitlab
 
         status_code = Gitlab::PollingInterval.polling_enabled? ? 304 : 429
 
-        [status_code, { 'ETag' => etag }, ['']]
+        [status_code, { 'ETag' => etag }, []]
       end
 
       def track_cache_miss(if_none_match, cached_value_present, route)

spec/lib/gitlab/etag_caching/middleware_spec.rb

@@ -91,6 +91,12 @@ describe Gitlab::EtagCaching::Middleware do
       expect(status).to eq 304
     end
 
+    it 'returns empty body' do
+      _, _, body = middleware.call(build_env(path, if_none_match))
+
+      expect(body).to be_empty
+    end
+
     it 'tracks "etag_caching_cache_hit" event' do
       expect(Gitlab::Metrics).to receive(:add_event)
         .with(:etag_caching_middleware_used, endpoint: 'issue_notes')