title: AdonisJS 5 - preload model even if foreign key is null
body: <p>I want to preload a model even if it have a null foreign key.
  I'll use the models from Adonis docs page to ilustrate: User and Profile.</p>
  <pre><code>const user = await User.query().preload(&quot;profile&quot;)
  </code></pre>
  <p>Simple as that!</p>
  <p>But in my case, <strong>if a user have the key profile_id as null, it throws an exception</strong>, what means it only preload existing relationships (fair enough).</p>
  <p>To make clear, I not want to preload just users with existing foreign keys, I need <strong>both</strong> existing user related models <strong>and</strong> users with no models to preload.</p>
  <p>I have read and tested the examples from <a href="https://preview.adonisjs.com/guides/model-relations/introduction#preloading-relationship" rel="nofollow noreferrer">docs</a> page, but it haven't enough explanation about this case (or I just didn't found it).</p>
  <p>Any hints will be appreciated</p>