Papertrail and Carrierwave

Question

I have a model that use both: Carrierwave for store photos, and PaperTrail for versioning.

I also configured Carrierwave for store diferent files when updates (That's because I want to version the photos) with config.remove_previously_stored_files_after_update = false

The problem is that PaperTrail try to store the whole Ruby Object from the photo (CarrierWave Uploader) instead of simply a string (that would be its url)

(version table, column object)

---
first_name: Foo
last_name: Bar
photo: !ruby/object:PhotoUploader
  model: !ruby/object:Bla
    attributes:
      id: 2
      first_name: Foo1
      segundo_nombre: 'Bar1'
      ........

How can I fix this to store a simple string in the photo version?