static function populateDotmailerDataFields(&$fields, $activityId)
 {
     if (!empty($GLOBALS["DotMailerCiviCRMDataFieldsMapping"])) {
         foreach ($GLOBALS["DotMailerCiviCRMDataFieldsMapping"] as $entity => $mapping) {
             switch ($entity) {
                 case 'contact':
                     $contactId = CRM_Dotmailer_Utils::getContactIdForActivity($activityId);
                     $entityId = $params['id'] = $contactId;
                     break;
                 case 'activity':
                     $entityId = $params['id'] = $activityId;
                     break;
                 default:
                     # code...
                     break;
             }
             foreach ($mapping as $CiviField => $DotmailerField) {
                 $params['return.' . $CiviField] = 1;
             }
             $entityDetails = civicrm_api3($entity, 'get', $params);
             $entityValues = $entityDetails['values'][$entityId];
             foreach ($mapping as $CiviField => $DotmailerField) {
                 $fields[$DotmailerField] = $entityValues[$CiviField];
             }
         }
     }
 }