activerecord 4.0.4 when and find_by ignores custom foreign_key when searching for association = nil

activerecord_4.0.4_issue

#!/usr/bin/env ruby

unless File.exist?('Gemfile')
  File.write('Gemfile', <<-GEMFILE)
    source 'https://rubygems.org'
    # gem 'rails', github: 'rails/rails'
    gem 'rails'
    gem 'sqlite3'
  GEMFILE

  system 'bundle'
end

require 'bundler'
Bundler.setup(:default)

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

ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :firma

  create_table :jidelak do |t|
    t.integer :firma_key
  end
end

class Canteen < ActiveRecord::Base
  self.table_name = 'firma'

  has_many :meals, foreign_key: 'firma_key'
end

class Meal < ActiveRecord::Base
  self.table_name = 'jidelak'

  belongs_to :canteen, foreign_key: 'firma_key'
end

class BugTest < Minitest::Spec
  def setup
    @canteen = Canteen.create!

    @meal1 = Meal.create!(canteen: @canteen)
    @meal2 = Meal.create!()
  end

  def teardown
    Canteen.delete_all
    Meal.delete_all
  end

  def test_finds_records_with_association
    assert_equal [@meal1], Meal.where(canteen: @canteen)
    assert_equal @meal1,   Meal.find_by(canteen: @canteen)
  end

  def test_finds_records_with_no_association
    assert_equal [@meal2], Meal.where(canteen: nil)
    assert_equal @meal2,   Meal.find_by(canteen: nil)
  end
end