alba: Can't get root_key to work (without inference)

Describe the bug

:root_key does not seem to be doing what I expect, I can’t get it to have an effect. I am not using inference, but still expect to be able to specify a root key manually.

To Reproduce

class MyThing
  attr_accessor :name
  def initialize(name:)
    @name = name
  end
end

class TestSerializer
  include Alba::Resource

  root_key :widget

  attributes :name
end

TestSerializer.new( MyThing.new(name: "joe") ).serializable_hash
# => {:name=>"joe"}

Expected behavior

I expected there to be a root key in the output, like

{ widget: {:name=>"joe"} }

Actual behavior

There is no root key in the output, just {:name=>"joe"}. The root_key seems to be ignored?

This also means I can’t get meta to output, because it requires a recognized root_key.

Additional context

Alba 1.6.0

I know the root_key function is integrated with “inference”, I am not using alba inference, not calling Alba.enable_inference!, not sure if that matters.