/**
  * This method returns the NDC for this event. It will return the
  * correct content even if the event was generated in a different
  * thread or even on a different machine. The {@link LoggerNDC::get()} method
  * should <b>never</b> be called directly.
  * @return string  
  */
 public function getNDC()
 {
     if ($this->ndcLookupRequired) {
         $this->ndcLookupRequired = false;
         $this->ndc = Payone_Log4php_LoggerNDC::get();
     }
     return $this->ndc;
 }