cart_itemが入っていなければ次のページへ遷移できなくする方法

<div class="container">
  <div class="row">
    <div class="col-10">
      <div class="row my-4">
        <div class="col-6">
        <h3 class="">ショッピングカート</h3>
        </div>
        <div class="col-6 text-right">
        <%= link_to "カートを空にする", public_all_destroy_path, method: :delete, class:"btn btn-danger" %>
        </div>
      </div>
      <div class="row">
        <table class="table col-12 table-bordered">
          <thead class="bg-light">
            <tr>
              <th class="text-center">商品名</th>
              <th class="text-center">単価（税込）</th>
              <th class="text-center">数量</th>
              <th class="text-center">小計</th>
              <th></th>
            </tr>
          </thead>
          <% @cart_items.each do |cart_item| %>
          <tbody>

            <td class="text-center"><%= image_tag cart_item.item.image, size: "70x50" %><%= cart_item.item.name %></td>

            <td class="text-center"><%= cart_item.item.add_tax_price.to_s(:delimited, delimiter: ',') %></td>

            <%= form_with model: cart_item, url: public_cart_item_path(cart_item.id) do |f| %>
            <td class="text-center"><%= f.select:amount,[[cart_item.amount],['1',1],['2',2],['3',3],['4',4],['5',5],['6',6],['7',7],['8',8],['9',9],['10',10]],class:"mr-1" %><%= f.submit "変更", class:"btn btn-success ml-1" %></td>
            <% end %>

            <td class="text-center"><%= (cart_item.item.add_tax_price*cart_item.amount).to_s(:delimited, delimiter: ',') %></td>

            <td class="text-center"><%= link_to "削除する", public_cart_item_path(cart_item.id),method: :delete, class:"btn btn-danger" %></td>
          </tbody>
          <% end %>
        </table>
      </div>
    </div>
  </div>
</div>
<div class="container">
  <div class="row">
    <div class="col-6 text-left">
      <%= link_to "買い物を続ける", public_root_path, class:"btn btn-primary ml-4" %>
    </div>
    <table class="table table-bordered col-2 text-right ml-5">
      <tr>
        <th class="bg-light text-center">合計金額</th>
        <td class="text-center"><%= @total_price.to_s(:delimited, delimiter: ',') %></td>
      </tr>
    </table>
  </div>
</div>
<div class="container mt-4">
  <div class="row justify-content-center">
    <div class="col-10 ">
      <div class="text-center">
       <%= link_to "情報入力に進む", new_public_order_path, class:"btn btn-success ml-4" %>
      </div>
    </div>
  </div>
</div>

class Public::CartItemsController < ApplicationController
  def index
    @cart_items=current_customer.cart_items.all
    @total_price=0
    @cart_items.each do |cart_item|
      @total_price += cart_item.item.add_tax_price*cart_item.amount
    end
  end

  def create
    cart_item=CartItem.new(cart_item_params)
    cart_item.customer_id=current_customer.id
    cart_item.save
    redirect_to public_cart_items_path(cart_item.id)
  end

  def update
    cart_item=CartItem.find(params[:id])
    cart_item.update(cart_item_params)
    redirect_to  public_cart_items_path(cart_item.id)
  end

  def destroy
    cart_item=CartItem.find(params[:id])
    cart_item.destroy
    redirect_to public_cart_items_path
  end

  def all_destroy
    cart_items=current_customer.cart_items
    cart_items.destroy_all
    redirect_to public_cart_items_path
  end

 private

  def cart_item_params
    params.require(:cart_item).permit(:item_id, :amount)
  end
end

<% if @cart_items == nil %>
<% render public_cart_items_path %>#今現在のページ
<% else %>
<% redirect_to  new_public_order_path %>#情報入力ページ
<% end %>