title: Eager loading nested relationships only if main relationship exists
body: <p>I am trying to load a nested realtionship from a model that can have or not a &quot;main&quot; relationship.</p>
  <p>I have 3 models: Building, Address and City.</p>
  <p>I have a Building model that <strong>optionally</strong> can have an Address relationship.</p>
  <p>If the Address relationship exists it <strong>always</strong> have a City relationship itself.</p>
  <p>My &quot;list buildings&quot; controller function looks as follow:</p>
  <pre><code>$buildingList = Building::with(['address','type'])-&gt;get();
  </code></pre>
  <p>The problem is this way the City nested relationship isn't loaded, so I did try the following:</p>
  <pre><code>$buildingList = Building::with(['address.city','type'])-&gt;get();
  </code></pre>
  <p>This way I get an error for every Building that hasn't an Address related model.</p>
  <p>Is there an elegant way to solve this?</p>