[Patch] Rails3 - accepts_nested_attributes_for reject_if => {blank id} raises ActiveRecord::RecordNotFound when id is an empty string

This happens if there is a select list to choose an existing 'task' id, with :include_blank => true, and the user submits the form with the blank task selected.

class Project < ActiveRecord::Base
  has_many :tasks
  accepts_nested_attributes_for :tasks, :reject_if => proc { |attributes| attributes[:id].blank? } 
end

class Task < ActiveRecord::Base
  belongs_to :project
end

p = Project.new(:name => "project", :tasks_attributes => {"0" => {"name" => "new name", "id" => ""}})
p.save

=> ActiveRecord::RecordNotFound (Couldn't find Account with ID= [WHERE (`accounts`.`deleted_at` IS NULL)]):

We traced the problem to activerecord/lib/active_record/nested_attributes.rb in the assign_nested_attributes_for_one_to_one_association method, at line 326:

elsif attributes['id']

should be

elsif not attributes['id'].blank?

(Note: assign_nested_attributes_for_collection_association uses attributes['id'].blank? already at line 395)

This is on Rails 3.0.0

Patch is attached (including test), or on my rails fork: http://github.com/ndbroadbent/rails/commit/f13a5674885f3d3388b5bc03...