Carrierwave hits update with unchanged value

[airled]

Hi there.
Chunk of my migration:

  ...
  t.json :gallery, null: false, default: {}

Mounting:

  mount_uploaders :gallery, AmusementGalleryUploader

Uploader:

class AmusementGalleryUploader < CarrierWave::Uploader::Base
  include CarrierWave::MiniMagick

  storage :file

  def store_dir
    "uploads/amusement/#{mounted_as}/#{model.id}"
  end

  def extension_whitelist
    %w[jpg jpeg gif png svg]
  end

  def content_type_whitelist
    [/image\//]
  end
end

The issue is if I try to update my record with form and image has same name (I do not even change anything else in my record), carrierwave with rails hit update on database even if array of images wasn't changed. Moreover, I use paper trail in my project so it creates unnecessary db record.
I inspect rails behaviour with before_save callback and byebug:

(byebug) self.changed?
true
(byebug) self.changes
{"gallery"=>[["screen-2020-04-11-12-42-10.jpg"], ["screen-2020-04-11-12-42-10.jpg"]]}

Logs of request:

Started PUT "/admin/amusement/3/edit" for ::1 at 2020-04-11 20:03:18 +0600
Processing by RailsAdmin::MainController#edit as HTML
  Parameters: **{"gallery"=>["screen-2020-04-11-12-42-10.jpg"]}**
  ...
  Amusement Update (1.1ms)  UPDATE "amusements" SET "gallery" = $1, "updated_at" = $2 WHERE "amusements"."id" = $3  [["gallery", "[\"screen-2020-04-11-12-42-10.jpg\"]"], ["updated_at", "2020-04-11 14:03:19.020026"], ["id", 3]]
  PaperTrail::Version Create (0.8ms)  INSERT INTO "versions" ("item_type", "item_id", "event", "whodunnit", "object", "object_changes", "locale", "created_at") VALUES ($1, $2, $3, $4, $5, $6, $7, $8) RETURNING "id"  [["item_type", "Amusement"], ["item_id", 3], ["event", "update"], ["whodunnit", "1"], ["object", "---\ngallery: '[\"screen-2020-04-11-12-42-10.jpg\"]'], ["object_changes", "---\ngallery:\n- '[\"screen-2020-04-11-12-42-10.jpg\"]'\n- '[\"screen-2020-04-11-12-42-10.jpg\"]'\n"], ["locale", "ru"], ["created_at", "2020-04-11 14:03:19.020026"]]
   (24.7ms)  COMMIT
Redirected to http://localhost:3000/admin/amusement
Completed 302 Found in 205ms (ActiveRecord: 38.2ms | Allocations: 30207)

Or even if I just use irb:

irb(main):007:0> a = Amusement.last
irb(main):008:0> a[:gallery]
=> ["grapefruit-slice-332-332.jpg"]
irb(main):009:0> a.gallery = ["grapefruit-slice-332-332.jpg"]
irb(main):010:0> a.changed?
=> true
irb(main):011:0> a.changes
=> {"gallery"=>[["grapefruit-slice-332-332.jpg"], ["grapefruit-slice-332-332.jpg"]]}
irb(main):012:0> a.save!
Amusement Update (1.3ms)  UPDATE "amusements" SET "gallery" = $1, "updated_at" = $2 WHERE "amusements"."id" = $3  [["gallery", "[\"grapefruit-slice-332-332.jpg\"]"], ["updated_at", "2020-04-11 14:11:16.310387"], ["id", 4]]
PaperTrail::Version Create (1.4ms)  INSERT INTO "versions" ("item_type", "item_id", "event", "object", "object_changes", "locale", "created_at") VALUES ($1, $2, $3, $4, $5, $6, $7) RETURNING "id"  [["item_type", "Amusement"], ["item_id", 4], ["event", "update"], ["object", "---\ngallery: '[\"grapefruit-slice-332-332.jpg\"]'], ["object_changes", "---\ngallery:\n- '[\"grapefruit-slice-332-332.jpg\"]'\n- '[\"grapefruit-slice-332-332.jpg\"]'\n"], ["locale", "ru"], ["created_at", "2020-04-11 14:11:16.310387"]]

Does anyone know how to fix it properly?