Live preview not working at all with 4.1.0-dp3

protected function getPublishFormButtons(ChannelEntry $entry)
 {
  $buttons = [
   [
    'name' => 'submit',
    'type' => 'submit',
    'value' => 'save',
    'text' => 'save',
    'working' => 'btn_saving'
   ],
   [
    'name' => 'submit',
    'type' => 'submit',
    'value' => 'save_and_new',
    'text' => 'save_and_new',
    'working' => 'btn_saving'
   ],
   [
    'name' => 'submit',
    'type' => 'submit',
    'value' => 'save_and_close',
    'text' => 'save_and_close',
    'working' => 'btn_saving'
   ]
  ];

  // get rid of Save & New button if we've reached the max entries for this channel
  if ($entry->Channel->max_entries != 0 && $entry->Channel->total_records >= $entry->Channel->max_entries)
  {
   unset($buttons[1]);
  }

  $has_preview_button  = FALSE;
  $show_preview_button = FALSE;

  if ($entry->hasLivePreview())
  {
   $has_preview_button  = TRUE;
   $show_preview_button = TRUE;
  }

  $pages_module = ee('Addon')->get('pages');
  if ($pages_module && $pages_module->isInstalled())
  {
   $has_preview_button = TRUE;
   if ($entry->hasPageURI())
   {
    $show_preview_button = TRUE;
   }
  }

  if ($has_preview_button)
  {
   $extra_class = ($show_preview_button) ? '' : ' hidden';

   $buttons[] = [
    'name'    => 'submit',
    'type'    => 'submit',
    'value'   => 'preview',
    'text'    => 'preview',
    'class'   => 'action js-modal-link--side' . $extra_class,
    'attrs'   => 'rel=live-preview',
    'working' => 'btn_previewing'
   ];
  }

  return $buttons;
 }

$site_id    = ee()->config->item('site_id');