Showing app/views/presences/_form.html.erb where line #1 raised: 
undefined method `model_name' for NilClass:Class

1: <%= form_for(@presence) do |f| %>
2:   <% if @presence.errors.any? %>
3:     <div id="error_explanation">
4:       <h2><%= pluralize(@presence.errors.count,"error") %> prohibited this presence from being saved:</h2>

这有什么不对？我从不调用一个名为“model_name”的方法,这段代码是自动化的,为什么它不起作用呢？@H_502_5@

谢谢@H_502_5@