file is prefixed and can't be shown

[UmPlat]

Mac Sequoia, Rails 8, ruby 3.3.5, gem carrierwave version 3.07, sqlite

When serialize :avatars, JSON in Post model.
rails c:
post = Post.last
raises `class:Post': wrong number of arguments (given 2, expected 1) (ArgumentError)

ChatGpt advices to comment this line for Rails 8.
Err gone and
rails c:
post = Post.last
files = [
File.open(Rails.root.join('storage', 'Carolyn1.jpg'))
]
post.avatars = files
post.save!
post.avatars.map(&:url) #["/uploads/post/avatars/9/Carolyn1.jpg"]

But when get /posts

I see prefix and suffix around the file and img can't be shown

[UmPlat]

I found solution:
just add
attribute :avatars, :json, default: []
to a model