/**
  * Sets the distance matrix request region.
  *
  * @param string $region The distance matrix request region.
  *
  * @throws \Ivory\GoogleMap\Exception\DistanceMatrixException If the region is not valid.
  */
 public function setRegion($region = null)
 {
     if ((!is_string($region) || strlen($region) !== 2) && $region !== null) {
         throw DistanceMatrixException::invalidDistanceMatrixRequestRegion();
     }
     $this->region = $region;
 }