ActiveStorage::Attachment - Unhandled case where named_variants can be nil

[CKolkey]

In ActiveStorage::Attachment, the private method named_variants can return nil, but callers of this method do not guard against a nil value being returned.

rails/activestorage/app/models/active_storage/attachment.rb

Lines 158 to 160 in bd04126

	def named_variants
	record.attachment_reflections[name]&.named_variants
	end

rails/activestorage/app/models/active_storage/attachment.rb

Line 135 in bd04126

preprocessed_variations = named_variants.filter_map { |_name, named_variant|

Steps to reproduce

# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"
  gem "rails"
  gem "sqlite3", "~> 1.4"
  gem "debug"
end

require "active_record/railtie"
require "active_storage/engine"
require "tmpdir"

class TestApp < Rails::Application
  config.load_defaults Rails::VERSION::STRING.to_f

  config.root = __dir__
  config.hosts << "example.org"
  config.eager_load = false
  config.session_store :cookie_store, key: "cookie_store_key"
  config.secret_key_base = "secret_key_base"

  config.logger = Logger.new($stdout)
  Rails.logger  = config.logger

  config.active_storage.service = :local
  config.active_storage.service_configurations = {
    local: {
      root: Dir.tmpdir,
      service: "Disk",
    },
  }
end

ENV["DATABASE_URL"] = "sqlite3::memory:"

Rails.application.initialize!

require ActiveStorage::Engine.root.join("db/migrate/20170806125915_create_active_storage_tables.rb").to_s

ActiveRecord::Schema.define do
  CreateActiveStorageTables.new.change

  create_table :uploads, force: true do |t|
    t.bigint "blob_id", null: false
    t.index ["blob_id"], name: "index_uploads_on_blob_id"
  end
end

class Upload < ActiveRecord::Base
  belongs_to :blob, class_name: "ActiveStorage::Blob"
end

require "minitest/autorun"

class BugTest < Minitest::Test
  def test_no_named_variants
    blob = ActiveStorage::Blob.create(checksum: 0, byte_size: 0, filename: "example", content_type: "image/png")
    record = Upload.create(blob_id: blob.id)
    attachment = ActiveStorage::Attachment.create(blob:, record:, name: "attachment_example")

    assert_equal true, true
  end
end

Expected behavior

No exception should get raised if there are no named variants.

Actual behavior

eval error: undefined method 'each' for nil

System configuration

Rails version:
Rails 7.1.3.3

Ruby version:
ruby 3.3.1 (2024-04-23 revision c56cd86388) [arm64-darwin23]