/**
  * Get or set sent status for a
  * Quotation by Quotation number
  * @param  integer $no
  * @param  boolean $set
  * @return boolean
  */
 public function sent($no, $set = NULL)
 {
     $handle = $this->getHandle($no);
     if (!is_bool($set)) {
         return $this->client->Quotation_GetIsSent(array('quotationHandle' => $handle))->Quotation_GetIsSentResult;
     } else {
         if (!$set) {
             $this->client->Quotation_CancelSentStatus(array('quotationHandle' => $handle));
         } else {
             $this->client->Quotation_RegisterAsSent(array('quotationHandle' => $handle));
         }
     }
     return true;
 }