Problem with Rails3.1.1 in mass_assignment_authorizer

By accident I had Rails-3.1.1 installed by bundler. However, when I
discovered this mishap during my feature run I encountered this error
in many places:

wrong number of arguments (1 for 0) (ArgumentError)
      /home/byrnejb/.rvm/gems/ruby-1.8.7-p352/gems/activemodel-3.1.1/
lib/active_model/mass_assignment_security.rb:209:in
`mass_assignment_authorizer'
      /home/byrnejb/.rvm/gems/ruby-1.8.7-p352/gems/activemodel-3.1.1/
lib/active_model/mass_assignment_security.rb:209:in
`sanitize_for_mass_assignment'
      /home/byrnejb/.rvm/gems/ruby-1.8.7-p352/gems/activerecord-3.1.1/
lib/active_record/base.rb:1744:in `assign_attributes'
      /home/byrnejb/.rvm/gems/ruby-1.8.7-p352/gems/activerecord-3.1.1/
lib/active_record/base.rb:1567:in `initialize'
      /home/byrnejb/.rvm/gems/ruby-1.8.7-p352/gems/activerecord-3.1.1/
lib/active_record/reflection.rb:190:in `new'

Everything was working on Friday last with Rails-3.0.9 and no changes
to the code or the features have been made. I am therefore somewhat
curious as to what might be causing this. I previously had mass
assignment turned off in an initializer:

$ cat config/initializers/attr_accessible_nil.rb
#ActiveRecord::Base.send(:attr_accessible, nil)

So, I am wondering if this might be the cause of the problem. Note
that I have no intention of moving to Rails-3.1.1 at the moment. I am
just curious as to what would be causing this error.

I found my problem is a library I wrote to turn off mass assignment .
In it I am calling this:

  # override AR method
  def mass_assignment_authorizer
    if accessible == :all
      self.class.protected_attributes
    else
      super + ( accessible || [] )
    end
  end

Mass_assignment_authorizer has a different signature in Rails 3.1 thus
the problem. By my way of thinking the signature change means that we
should be talking of Rails-4.0.1 instead of Rails-3.1.1. But, then
again, given what has happened to Firefox perhaps not.

You can't expect every single internal rails method not to change
between rails versions (although public methods should certainly not
change signature like that).
One of the things 3.0 was supposed to bring was greater clarity about
what bits of the internals could be depended upon in this manner and
which couldn't. Part of that involved breaking up action controller
into more reusable components, but I'm not sure where things got to
with active record.

Fred