Ruby on rails 3 因为反射错误而导致json不工作

我有一个名为Foo的类，看起来像这样：

class Foo < ActiveRecord::Base 
  belongs_to othermodel 
end 

class Bar  < Foo 
   belongs_to thirdmodel
end 

---

问题出在斯芬克斯身上。移除它并用自己的解决方案替换它，现在它可以完美地工作

NoMethodError: undefined method `macro' for nil:NilClass
   from ~/.rvm/gems/ruby-1.9.2-p0/gems/activerecord-3.0.0/lib/active_record/serialization.rb:41:in `block in serializable_add_includes'