permission.rb in cancannible-2.0.0

- old
+ new

@@ -1,13 +1,12 @@
 # The Permission class stores permissions managed by CanCan and Cancannible
 class Permission < ActiveRecord::Base
   belongs_to :permissible, polymorphic: true
-  belongs_to :resource, polymorphic: true
+  belongs_to :resource, polymorphic: true, optional: true
 
+  validates :ability, uniqueness: { scope: [:resource_id, :resource_type, :permissible_id, :permissible_type] }
+
   # Note: for Rails 3 you may need to declare attr_accessible as follows, depending on your whitelist_attributes setting.
   # A future version of cancannible should make this unnecessary.
   #
   # attr_accessible :asserted, :ability, :resource_id, :resource_type
-
-  validates_uniqueness_of :ability, scope: [:resource_id, :resource_type, :permissible_id, :permissible_type]
-
-end
\ No newline at end of file
+end