title: Laravel: Collections gives error because of appends when that perticular field is not selected
body: <p>Laravel version: 5.7</p>
  <p>I have one class <code>Sessions</code>. where I have used appends for the attribute.</p>
  <pre><code>class Session extends Model
  {
    protected $appends    = ['session_type'];
  
    public function getSessionTypeAttribute()
    {
       $startTime = $this-&gt;getOriginal()['start_time'];
       return $startTime;
    }
  }
  </code></pre>
  <p>My query:</p>
  <pre><code>$sessions = Session::groupBy(DB::raw('YEAR(created_at), MONTH(created_at), visibility'))
                  -&gt;select(DB::raw('COUNT(id) as total,MONTH(created_at) as month,MONTHNAME(created_at) as month_name,visibility'))
                  -&gt;orderBy('created_at', 'ASC')
                  -&gt;get();
  </code></pre>
  <p>Here I have selected fields that I need but it gives me the following error.</p>
  <pre><code>Undefined index: start_time
  </code></pre>
  <p>So here appends are giving error because I have not selected start_time. How to solve this issue?</p>