title: Rails 5.2: Difference of if current_user vs current_user.present? in views
body: <p>I follow <a href="https://www.ombulabs.com/blog/benchmark/performance/rails/present-vs-any-vs-exists.html" rel="nofollow noreferrer">this post</a>. In my view:</p>
  
  <pre><code>- if current_user
  - if current_user.present?
  - if current_user.exists?
  - if current_user.any?
  </code></pre>
  
  <p>I get the error:</p>
  
  <pre><code>undefined method `exists?' for #&lt;User:0x00007fd68f4067b8&gt;
  undefined method `any?' for #&lt;User:0x00007fd68f4067b8&gt;
  </code></pre>
  
  <p>So only the first 2 work. Why? Is there any difference in performance of:</p>
  
  <pre><code>- if current_user
  vs
  - if current_user.present?
  </code></pre>
  
  <p>and</p>
  
  <pre><code>- if current_user.name
  vs
  - if current_user.name.present?
  </code></pre>