Notice: Use of undefined constant tab – assumed 'tab' in…

Hello,

I am getting the following notices no matter what the I tried with.

Notice: Use of undefined constant tab - assumed 'tab' in \wp-content\plugins\gplus-comments\templates\container.php on line 53

then I have replaced the following lines in container.php

<ul class="controls inline clearfix">
    <?php
      $tab_order = explode(',',$options['tab_order']);
      $active = ' class="active"';
      foreach ($tab_order as $tab) {
        echo "<li${active}><a href='#${tab}-tab'>";
        if(!$options['hide_icons'])
        {
          echo "<img src='".GPLUS_COMMENTS_URL."/images/icons/default/${tab}.png'>";
        }
        echo $options[${tab}.'_label']."</a></li>\n";
        $active = '';
      }
    ?>
  </ul>

to this,

<ul class="controls inline clearfix">
    <?php
      $tab_order = explode(',',$options['tab_order']);
      $active = ' class="active"';
      foreach ($tab_order as $tab) {
        echo "<li" . $active . "><a href='#". $tab . "-tab'>";
        if(!$options['hide_icons'])
        {
          echo "<img src='".GPLUS_COMMENTS_URL."/images/icons/default/" . $tab . ".png'>";
        }
        echo $options[$tab . '_label']."</a></li>\n";
        $active = '';
      }
    ?>
  </ul>

and it works as expected. Do you have any suggestion?

Kind regards.

https://www.ads-software.com/extend/plugins/gplus-comments/