Call to ActiveRecord::AssociationRelation#empty? returns false for an empty result set.

gistfile1.txt

# Activate the gem you are reporting the issue against.
gem 'activerecord', '4.1.0'
require 'active_record'
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 do |t|
  end
  
  create_table :posts do |t|
    t.integer :user_id
  end
end

class User < ActiveRecord::Base
  has_many :posts
end

class Post < ActiveRecord::Base
  belongs_to :user
end

class BugTest < Minitest::Test
  def test_empty_bug
    User.destroy_all
    Post.destroy_all

    user1 = User.create!
    user2 = User.create!

    post1 = Post.create!(user: user1)
    post2 = Post.create!(user: user1)
    post3 = Post.create!(user: user2)
    post4 = Post.create!(user: user1)

    posts = user2.posts.where(user_id: user1.id)
    assert_empty posts
  end
end