we can't see a nil category

lib/guardian/category_guardian.rb

@@ -45,6 +45,7 @@ module CategoryGuardian
   end
 
   def can_see_category?(category)
+    return false unless category
     return true if is_admin?
     return true if !category.read_restricted
     return true if is_staged? && category.email_in.present? && category.email_in_allow_strangers