title: Error exception 'InvalidArgumentException' in Laravel
body: <p>I have a strange problem with Laravel's schedule that I am trying to solve:</p>
  
  <pre><code>ERROR: exception 'InvalidArgumentException' with message 'Invalid scheduled callback event. Must be string or callable'.
  </code></pre>
  
  <p>This is the line of Kernel.php:</p>
  
  <pre><code>$schedule-&gt;call(\App\Classes\Maintenance::deleteAllRecord())-&gt;daily();
  </code></pre>
  
  <p>And this is the function :</p>
  
  <pre><code>public static function deleteAllRecord()
  {
      $data=\App\LastSeen::all();
      foreach ($data as $dt)
      {
          $dt-&gt;delete();
      }
      return 'OK';
  }
  </code></pre>
  
  <p>I try also return true , but I had the same problem.I'm sure that the problem is the type of return. Where I make the mistake ? 
  I hope I was exhaustive. I wait answer ^_^ have a good day.</p>