使用 rails-simple-search 这个 gemhttps://github.com/yzhanginwa/rails-simple-search 用作搜索，但是在 rails 4.2 报错，出现一下错误：

NoMethodError - undefined method `param_key' for nil:NilClass:
  actionview (4.2.0) lib/action_view/helpers/form_helper.rb:433:in `form_for'

应该是这里出问题

@search = Search.new(User, params[:search])

<% form_for @search, url => "/xxxxxx" do |f| %>

在 google 搜索过， http://stackoverflow.com/questions/27429276/rails-4-and-form-for-undefined-method-param-key-for-nilnilclass

Hey I figured it out.. Style belongs to :model which is throwing an error because of some .model_name stuff in Rails 4 .. That was a poor choice for a model name! Now to rewrite my db, model, controllers, views, etc 

但是我不知道具体问题出现在他代码哪里？要怎么修改？ 请教大家！