Rack app error: #<Errno::ENOENT: No such file or directory - log/oink.log> Heroku Padrino app

[kakubei]

On Heroku, with a Padrino app I get this error trying to initialize the app:

Rack app error: #<Errno::ENOENT: No such file or directory - log/oink.log>

Configuration of Oink in app/app.rb is as follows:

  use Oink::Middleware do
    set :logger => Hodel3000CompliantLogger.new(STDOUT)
  end

Which I got from the docs.

How can I fix this?

Thanks.