Add missing require to active_support/callbacks.rb

[okuramasafumi]

Summary

At line 353, blank? method is called.
We need to require "active_support/core_ext/object/blank" for blank? to be available.

Other Information

This is a fix for a subtle bug in ActiveSupport::Callbacks.
It was (at least I think) trivial so I didn't create an issue for it but instead fixed it in this PR.

require 'active_support/callbacks'

class Record
  include ActiveSupport::Callbacks
  define_callbacks :save

  def save
    run_callbacks :save do
      puts "- save"
    end
  end
end

class PersonRecord < Record
  set_callback :save, :before, :saving_message
  def saving_message
    puts "saving..."
  end

  set_callback :save, :after do |object|
    puts "saved"
  end
end

This code (from Rails official doc plus require) doesn't work due to the error in version 6.1.3.1 of `activesupport'.

/Users/okuramasafumi/.gem/ruby/3.0.1/gems/activesupport-6.1.3.1/lib/active_support/callbacks.rb:356:in `check_conditionals': undefined method `blank?' for nil:NilClass (NoMethodError)

After adding require 'active_support/core_ext/object/blank' it started working as expected.

This bug seems to be introduced in 0740adb.