public function exportAttachmentsInArchive(Tracker_Artifact $artifact, ZipArchive $archive)
 {
     $file_fields = $this->form_element_factory->getUsedFileFields($artifact->getTracker());
     $last_changeset = $artifact->getLastChangeset();
     if (!$last_changeset) {
         return;
     }
     foreach ($file_fields as $field) {
         $value = $last_changeset->getValue($field);
         if ($value) {
             $this->addFilesIntoArchive($value, $archive);
         }
     }
 }