Rails6でDM機能を実装する方法。

前提・実現したいこと

Rails6.0.3でDM機能を実装中に以下のエラーメッセージが発生しました。

発生している問題・エラーメッセージ

ActionController::UrlGenerationError in RoomsController#create

No route matches {:action=>"show", :controller=>"rooms", :id=>nil}, missing required keys: [:id]

Parameters:
{"authenticity_token"=>"KS15OrvWiRrpsJHSybYAgUF64SK6hn/9xK5DyAkwr1/dg5yxKgwMiJKtjriDv3oWHKN3zQd300y4l5n9Tkh9Gg==", "entry"=>{"user_id"=>"1"}, "commit"=>"チャットを始める"}
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該当のソースコード

users_controller.rb

class UsersController < ApplicationController
  def show
    @user = User.find(params[:id])
    @microposts = @user.microposts
    @currentUserEntry=Entry.where(user_id: current_user.id)
    @userEntry=Entry.where(user_id: @user.id)
    unless @user.id == current_user.id
      @currentUserEntry.each do |cu|
        @userEntry.each do |u|
          if cu.room_id == u.room_id then
            @isRoom = true
            @roomId = cu.room_id
          end
        end
      end
      if @isRoom
      else
        @room = Room.new
        @entry = Entry.new
      end
    end
  end
end

app/views/users/show.html/erb

  <% unless @user.id == current_user.id %>
    <% if @isRoom == true %>
      <p class="user-show-room"><a href="/rooms/<%= @roomId %>" class="btn btn-primary btn-lg">チャットへ</a>
    <% else %>
      <%= form_for @room do |f| %>
        <%= fields_for @entry do |e| %>
          <%= e.hidden_field :user_id, value: @user.id %>
        <% end %>
        <%= f.submit "チャットを始める", class:"btn btn-primary btn-lg user-show-chat"%>
      <% end %>
    <% end %>
  <% end %>

rooms_controller.rb

class RoomsController < ApplicationController
  before_action :authenticate_user!

  def create
    @room = Room.create(:name => "DM")
    @entry1 = Entry.create(room_id: @room.id, user_id: current_user.id)
    @entry2 = Entry.create(params.require(:entry).permit(:user_id, :room_id).merge(room_id: @room.id))
    redirect_to room_path(@room.id)
  end

  def show
    @room = Room.find(params[:id])
    if Entry.where(user_id: current_user.id,room_id: @room.id).present?
      @messages = @room.messages
      @message = Message.new
      @entries = @room.entries
    else
      redirect_back(fallback_location: root_path)
    end
  end
end

routes.rb

Rails.application.routes.draw do
  devise_for :users, controllers:{   registrations: 'users/registrations',
                                     sessions: 'users/sessions' }

  resources :users , only: [:show]

  resources :microposts do
      resource :favorites, only: [:create, :destroy]
  end
  
  resources :messages, only: [:create]
  resources :rooms, only: [:create,:show]

  root 'public#home'
  get  'public/show'
  # For details on the DSL available within this file, see https://guides.rubyonrails.org/routing.html
end