title: Returing null value using all_to_array in codeigniter
body: <p>I was facing a problem with all_to_array. It's returning a null value. </p>
  
  <pre><code> $object_self = new self();
  
              $response = $object_self-&gt;
      select('DATE(`created_at`) as `day`')-&gt;select_min('paid_amount','min_amount')
  -&gt;get('orders');
  
               $query_object = $response-&gt;all_to_array(array(
                                                                  'day',
                                                                  'min_amount',
  
                                                     ));
  </code></pre>
  
  <p>The $query_object is a null value all though the query is correct.</p>