/**
  * Get value.
  *
  * @param array $values
  * @param null $currency
  * @return mixed
  */
 private function getValue(array $values, $currency = null)
 {
     $currency = !is_null($currency) ? strtolower($currency) : $this->provider->get();
     $values = array_change_key_case($values);
     return $values[$currency];
 }