How to upload a photo from a Rails cache hash?

Question

I'm quite new with Rails and I'm trying to implement a multistep form in my app for creating a new instance of my User model (devise gem).

I use wicked gem and I've chosen a cache persistence and an ID/Key-in-Session as strategies to handle it.

For now, everything works well until I come across the avatar step in my form which is my last one (a @user has_one_attached :avatar).

When I try to submit my form, I got the below issue raising from that line: Rails.cache.write(session.id, user_attrs)

TypeError in Users::UserStepsController#update
can't dump File

Here my user_attrs when I submit my picture:

{"messenger_id"=>"1234567890123456",
"form_step"=>:profile_picture_step,
"first_name"=>"John",
"last_name"=>"Doe",
"email"=>"[email protected]",
"password"=>"1234",
"password_confirmation"=>"1234",
"avatar"=>#<ActionDispatch::Http::UploadedFile:0x00007fbdc4cdf418
  @tempfile=#<Tempfile:/var/folders/m_/8ln6gczs1ns1gnn53p6vskwr0000gn/T/RackMultipart20210527-5416-uy59kl.png>,
  @original_filename="Screenshot 2021-05-26 at 20.34.43.png", @content_type="image/png",
  @headers="Content-Disposition: form-data; name=\"user[avatar]\"; filename=\"Screenshot 2021-05-26 at 20.34.43.png\"\r\nContent-Type: image/png\r\n">}

It seems Rails.cache.write is not able to write this avatar object, am I right? If so, is there a way to fix it?

Thank you for your help!