title: PHP function stripos() expects parameter 1 to be string, object given
body: <p>I'm running through Laravel 6.0's <code>addSelect()</code> method as the official documentation described. However, I'm getting an error as my title suggested.  </p>
  
  <p>Two corresponding tables are: </p>
  
  <pre class="lang-sql prettyprint-override"><code>CREATE TABLE `destinations` (
   `id` int(11) NOT NULL AUTO_INCREMENT,
   `name` varchar(90) NOT NULL,
   PRIMARY KEY (`id`)
  ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=latin1
  
  CREATE TABLE `flights` (
   `id` int(11) NOT NULL AUTO_INCREMENT,
   `name` varchar(90) NOT NULL,
   `destination_id` int(11) NOT NULL,
   `arrived_at` datetime NOT NULL,
    PRIMARY KEY (`id`)
  ) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=latin1
  </code></pre>
  
  <p>The corresponding controller:</p>
  
  <pre class="lang-php prettyprint-override"><code>use App\Flight;
  use App\Destination;
  
  class TestController extends Controller
  {
      public function Index()
      {
          return Destination::addSelect(['last_flight' =&gt; 
              Flight::select('name')
              -&gt;whereColumn('destination_id', 'destinations.id')
              -&gt;orderBy('arrived_at', 'desc')
              -&gt;limit(1)
          ])-&gt;get();
      }
  }
  </code></pre>
  
  <p>What is the object provided as a parameter, which is responsible for the error?</p>