title: firstOrFail() function behaviour in Laravel
body: <p>I have a factory with this line in it:</p>
  
  <pre><code>$channel = \App\Model\Channel::firstOrFail();
  </code></pre>
  
  <p>How is the id set?
  I know there is a function like</p>
  
  <pre><code>$channel = \App\Model\Channel::firstOrFail($id);
  </code></pre>
  
  <p>But what's the difference to the one above and how do you set it?</p>