Documentation for ResourceSerializer with includes is incorrect

v0.10 serializer guideのincludeセクションから始め、その例をtest/unit/serializer/serializer_test.rbの205〜226行付近と比較してください。ドキュメントに記載されたResourceSerializerの呼び出しを再現し、そのうえでドキュメントとserializerの動作のどちらが誤っているのかを判断してください。ドキュメントに記載されたincludeワークフローが正確で、焦点を絞ったテストでカバーされていれば完了です。

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The documentation says that ResourceSerailizer should be able to include resources by doing something like this:

post = Post.find(1)

JSONAPI::ResourceSerializer.new(PostResource,
  include: ['comments'],
).serialize_to_hash(PostResource.new(post, nil))

But when I do this I don't get an included section in the serialized output.

Additionally I don't find any tests in the test suite that demonstrate the documented way of doing it, but I find several tests that seem to achieve includes via much more verbose and laborious methods.

Am I missing something?