/**
  * Create an Upgrade record.
  *
  * @since 1.0
  *
  * @param Activation $activation
  * @param Release    $release
  * @param \DateTime  $update_date
  * @param string     $previous_version
  *
  * @return Update|null
  * @throws DB_Exception
  */
 public static function create(Activation $activation, Release $release, \DateTime $update_date = null, $previous_version = '')
 {
     if ($update_date === null) {
         $update_date = make_date_time();
     }
     if (empty($previous_version) && $activation->get_release()) {
         $previous_version = $activation->get_release()->get_version();
     }
     $data = array('activation' => $activation->get_id(), 'release_id' => $release->get_ID(), 'update_date' => $update_date->format("Y-m-d H:i:s"), 'previous_version' => $previous_version);
     $db = Manager::make_simple_query_object('itelic-updates');
     $ID = $db->insert($data);
     $update = self::get($ID);
     if ($update) {
         $activation->set_release($release);
         /**
          * Fires when an update record is created.
          *
          * @since 1.0
          *
          * @param Update $update
          */
         do_action('itelic_create_update', $update);
         Cache::add($update);
     }
     return $update;
 }