/**
  * Get default thumb url
  * @return string|NULL
  * @author Panagiotis Vagenas <*****@*****.**>
  * @since 1.0.0
  */
 public function getDefaultThumbnail()
 {
     if ($this instanceof erpPROMainOpts) {
         $t = $this->getValue('defaultThumbnail');
     } else {
         erpPROPaths::requireOnce(erpPROPaths::$erpPROMainOpts);
         $mOpts = new erpPROMainOpts();
         $t = $mOpts->getDefaultThumbnail();
     }
     return !empty($t) ? $t : erpPRODefaults::$comOpts['defaultThumbnail'];
 }