Implements Drupal\Core\TypedData\ComplexDataInterface::get().
Overrides ComplexDataInterface::get
public function get($property_name) {
  $elements = $this
    ->getElements();
  if (isset($elements[$property_name])) {
    return $elements[$property_name];
  }
  else {
    throw new InvalidArgumentException(format_string("The configuration property @key doesn't exist.", array(
      '@key' => $property_name,
    )));
  }
}