rails s エラーが出る Completed 500 Internal Server Error

Question

Started GET "/" for 127.0.0.1 at 2020-03-20 11:41:13 +0900
Processing by RoomsController#show as */*
  Rendering rooms/show.html.erb within layouts/application
  Message Load (0.2ms)  SELECT "messages".* FROM "messages"
  ↳ app/views/rooms/show.html.erb:3
  Rendered collection of messages/_message.html.erb [2 times] (Duration: 0.1ms | Allocations: 20)
  Rendered rooms/show.html.erb within layouts/application (Duration: 6.8ms | Allocations: 913)
Completed 500 Internal Server Error in 20ms (ActiveRecord: 0.2ms | Allocations: 6961)

rails sと起動したが画面にこのように出てしまう。
show.html.erb

<h1>Chat Room</h1> <div id="messages"> <%= render @messages %> </div>

↑
が画面に表示されるはずがされなくなってしまった。