Get a collection through ActiveRecord for using with option_

Hello,

I am having some difficulties with ActiveRecord.

What I want to do is to get a collection of SubjectGroups for using
with option_groups_from_collection_for_select

My Code:

========================================
class Subject < ActiveRecord::Base
has_and_belongs_to_many :users
belongs_to :subject_group
end

class SubjectGroup < ActiveRecord::Base
has_many :subjects
end

@subjects= Subject.find(:all, :include => :subject_group)
@groups= SubjectGroup.find(:all, :include => :subjects)

The first find instruction runs just fine, the second gives me the
following error:

You have a nil object when you didn’t expect it!, The error occurred
while evaluating nil.loaded

I was expecting a SubjectGroup collection with all Subjects associated.

In both cases I saw the generated queries through logs and returns the
same query result.

Thank you for your attention,

Paulo A.