camelize_keys doesnt' camelize nested keys

[apuntovanini]

#652 introduced camelize_keys, which is great especially if you expose rabl results to react component for instance. The problem is that it doesn't camelize nested keys.
I added failing tests

context "when keys are camelized" do
  setup do
    Rabl.configuration.camelize_keys = true
    builder(nil, { :attributes => [ { :name => :first_pets_name }], :node => [{ :name => :preferences, :block => lambda { |u| { has_visible_profile: true } } }] })
  end
  asserts "that the key is camelized" do
    topic.to_hash(User.new)
  end.equivalent_to({ :firstPetsName => 'jack', preferences: { hasVisibleProfile: true } })
  teardown do
    Rabl.configuration.camelize_keys = false
  end
end

context "when keys are camelized with upper case first letter" do
  setup do
    Rabl.configuration.camelize_keys = :upper
    builder(nil, { :attributes => [ { :name => :first_pets_name }], :node => [{ :name => :preferences, :block => lambda { |u| { has_visible_profile: true } } }] })
  end
  asserts "that the key is camelized with upper case first letter" do
    topic.to_hash(User.new)
  end.equivalent_to({ :FirstPetsName => 'jack', Preferences: { HasVisibleProfile: true } })
  teardown do
    Rabl.configuration.camelize_keys = false
  end
end

I can't trace where the hash is parsed and names are set, can anyone help me out with this?
Thanks!