Accessing belongs_to association without a key creates a useless query

Environment

• Ruby 3.2.2
• Rails 7.1.1
• ActiveHash 3.2.1

Problem

When accessing a belongs_to association, if the related id is missing then a query for id IS NULL is made. This is different from the standard ActiveRecord behaviour and I think in 99% of cases a redundant query. Seems to be caused by the internal use of find_by_id with a blank argument: https://github.com/active-hash/active_hash/blob/master/lib/associations/associations.rb#L177

You can reproduce and observe with this script:

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "rails", "7.1.1"
  gem "sqlite3"
  gem "active_hash", "3.2.1"
end

require "active_hash"
require "active_record"
require "logger"

ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: "db/development.sqlite3")
ActiveRecord::Schema.define do
  create_table :authors, force: true
  create_table :magazines, force: true do |t|
    t.belongs_to :author, null: true
  end
end

class Author < ActiveRecord::Base
end

class Book < ActiveHash::Base
  include ActiveHash::Associations

  fields :author_id

  belongs_to :author
end

class Magazine < ActiveRecord::Base
  belongs_to :author, optional: true
end

book = Book.new(author_id: nil)
magazine = Magazine.create!(author_id: nil)

ActiveRecord::Base.logger = Logger.new(STDOUT)

puts "-" * 50
puts "Accessing ActiveHash association with NULL key"
book.author
puts "-" * 50
puts "Accessing ActiveRecord association with NULL key"
magazine.author
puts "-" * 50

Potential Solution

Don't bother querying if the key is NULL, if there is some weird edge case where you would want this then perhaps the behaviour could be enabled with a config option or optional argument when defining the association.

Start with lib/associations/associations.rb around line 177 and run the reproduction script from the issue using Rails 7.1.1, SQLite, and ActiveHash 3.2.1. Compare the ActiveHash and ActiveRecord association logs when author_id is nil. Done means the ActiveHash association no longer issues the id IS NULL query while preserving association access behavior.