class GdsApi::PublishingApi

def get_linkables(document_type: nil)

Other tags:
    See: https://github.com/alphagov/publishing-api/blob/master/doc/api.md#get-v2linkables - 
def get_linkables(document_type: nil)
  if document_type.nil?
    raise ArgumentError.new("Please provide a `document_type`")
  end
  get_json("#{endpoint}/v2/linkables?document_type=#{document_type}")
end