<% articles.each do |article| %>
  <div>
    <h1><%= link_to article.title, article %></h1>
    <p><%= article.subtitle %></p>
    <p>Category: <%= link_to article.category_name, article.category %></p>
    <p>
      Tags: 
      <% article.tags.each do |tag| %>
        <span><%= link_to tag.name, tag %></span>
      <% end %>
    </p>
  </div>
<% end %>

<% articles.each do |article| %>
  <div>
    <h1><%= link_to article.title, article %></h1>
    <p><%= article.subtitle %></p>
    <% if article.category %>
      <p>Category: <%= link_to article.category_name, article.category %></p>
    <% end %>
    <p>
      Tags: 
      <% article.tags.each do |tag| %>
        <span><%= link_to tag.name, tag %></span>
      <% end %>
    </p>
  </div>
<% end %>

Fix could not show no category article
Fix could not show no category article
