I had the same error when using self.inherited. ActiveRecord::Base also defines this method, not only included – calling super solved the problem with “can’t dup NilClass”. Great post, thanks.

Rails 2.3.5

Problem: Dev mode wants to reload before every request. Rails initialization gets messed up when reloading code from plugins and monkeypatches. The plugin or patch isn’t loaded at all or, if it is, things that you expect to be defined at reload time aren’t.

My case: monkeypatching the Tag model in acts_as_taggable_on_steroids to add a has_many association

Solution: Wrap the monkeypatch code in:

require ‘dispatcher’
Dispatcher.to_prepare do
Tag.class_eval do
# patches
end
end

Resources:
http://stackoverflow.com/questions/2397740/how-to-extend-an-unloadable-rails-plugin
http://www.oliyiptong.com/blog/2008/08/22/rails-to_prepare-executing-code-before-each-request/

Just another option in case you don’t want to edit environment.rb.

oh_noes = nil
Time.parse(oh_noes)

I assume the parse method dupes the value to make sure it doesn’t modify yours, hence the error.

This is what caused ours. Likewise I assume any method that tries to dup without checking for nil first will throw this.

Paul’s solution works nicely for me.

Paul:

Second, you could put something like this in your application’s environment.rb file:
config.reload_plugins = true if RAILS_ENV == ‘development’

See http://groups.google.com/group/rubyonrails-talk/browse_thread/thread/f54f18f4d4354926?pli=1 for an explanation.

In environment.rb:

Rails::Initializer.run do |config|
# etc
config.to_prepare do
# use load to ensure the added functionality is actually evaluated every time
load 'path/to/your/extension.rb'
end
end