An instance of ActionController::Parameters stored in a column as YAML with Rails 4, cannot be read with Rails 5.

store-issue-rails-4.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  # Activate the gem you are reporting the issue against.
  gem 'activerecord', '4.2.6'
  gem 'actionpack', '4.2.6'
  gem 'sqlite3'
end

require 'active_record'
require 'action_controller'
require 'minitest/autorun'
require 'logger'

# Ensure backward compatibility with Minitest 4
Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :users, force: true do |t|
    t.text :preferences
  end
end

class User < ActiveRecord::Base
  store :preferences, accessors: [
    :color,
    :font
  ]
end

class BugTest < Minitest::Test
  def test_serialization
    user = User.create!(
      preferences: ActionController::Parameters.new(color: "red", font: "Times")
    )

    user = user.reload

    assert_equal(
      "--- !ruby/hash-with-ivars:ActionController::Parameters\nelements:\n  color: red\n  font: Times\nivars:\n  :@permitted: \n",
      user.read_attribute_before_type_cast(:preferences)
    )

    assert_equal(Hash, user.preferences.class)
  end
end

# Output
#
# BugTest#test_serialization [store-issue-rails-4.rb:54]:
# Expected: Hash
#   Actual: ActionController::Parameters

store-issue-rails-5.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  # Activate the gem you are reporting the issue against.
  gem 'activerecord', '5.0.0'
  gem 'actionpack', '5.0.0'
  gem 'sqlite3'
end

require 'active_record'
require 'action_controller'
require 'minitest/autorun'
require 'logger'

# Ensure backward compatibility with Minitest 4
Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :users, force: true do |t|
    t.text :preferences
  end
end

class User < ActiveRecord::Base
  store :preferences, accessors: [
    :color,
    :font
  ]
end

class BugTest < Minitest::Test
  def test_serialization
    user = User.create!
    User.connection.execute(
      "UPDATE users SET preferences = '--- !ruby/hash-with-ivars:ActionController::Parameters\nelements:\n  color: red\n  font: Times\nivars:\n  :@permitted: \n';"
    )

    user = user.reload

    assert_equal(
      "--- !ruby/hash-with-ivars:ActionController::Parameters\nelements:\n  color: red\n  font: Times\nivars:\n  :@permitted: \n",
      user.read_attribute_before_type_cast(:preferences)
    )

    assert_equal(Hash, user.preferences.class)
  end
end

# Output
#
# BugTest#test_serialization:
# NoMethodError: undefined method `[]=' for nil:NilClass
#     /Users/bquorning/.gem/ruby/2.3.1/gems/actionpack-5.0.0/lib/action_controller/metal/strong_parameters.rb:414:in `[]='
#     /Users/bquorning/.rubies/ruby-2.3.1/lib/ruby/2.3.0/psych/visitors/to_ruby.rb:362:in `block in revive_hash'
#     /Users/bquorning/.rubies/ruby-2.3.1/lib/ruby/2.3.0/psych/visitors/to_ruby.rb:336:in `each'
#     /Users/bquorning/.rubies/ruby-2.3.1/lib/ruby/2.3.0/psych/visitors/to_ruby.rb:336:in `each_slice'
#     [...]