rom-mapper problem with reverse relationship

rom-mapper.rb

require 'rom-mapper'

class BigDecimal
  def inspect
    format("#<BigDecimal:%x %s>", object_id, to_s('F'))
  end
end

class Gateway
  def get_authors
    [
      {
        'name' => 'John Doe',

        'books' => [
          {
            'title' => 'First book',
            'price' => '15.99',
          },
          {
            'title' => 'Second book',
            'price' => '18.99',
          },
        ]
      }
    ]
  end
end

class Preprocessor < ROM::Mapper
  symbolize_keys true

  model name: 'Author'

  attribute :name

  embedded :books, type: :array do
    model name: 'Book'

    attribute :title
    attribute :price, type: :decimal
  end
end

module Repository
  class Authors
    class << self
      def all
        @@authors ||= preprocessor.call raw_authors
      end

      def find_by_name name
        all.detect { |author| author.name == name }
      end

      private

      def preprocessor
        Preprocessor.build
      end

      def raw_authors
        @@raw_authors ||= gateway.get_authors
      end

      def gateway
        @@gateway ||= Gateway.new
      end
    end
  end
end

authors = Repository::Authors.all

p authors
p authors.first.name
p authors.first.books.first.author.name

# outputs:
# [#<Author:0x007fc30e328060 @name="John Doe", @books=[#<Book:0x007fc30e328560 @title="First book", @price=#<BigDecimal:3fe18719438c 15.99>>, #<Book :0x007fc30e3281f0 @title="Second book", @price=#<BigDecimal:3fe1871941d4 18.99>>]>]
# "John Doe"
# rom-mapper.rb:77:in `<main>': undefined method `author' for #<Book:0x007fc30e328560> (NoMethodError)