title: Why do we need to use unless and "?" together instead of if alone
body: <p>what is the need for using unless and "?" together when you can use if like in this case</p>
  
  <pre><code>unless person.present?
  </code></pre>
  
  <p>is equivalent to </p>
  
  <pre><code>if person.present
  </code></pre>