protected function _getRateLimitInfo($headers)
  {
    if (! isset($headers['x-rate-limit-limit'])) {
      return null;
    }
    $rate = [
      'limit'     => $headers['x-rate-limit-limit'],
      'remaining' => $headers['x-rate-limit-remaining'],
      'reset'     => $headers['x-rate-limit-reset']
    ];
    if ($this->_return_format === CODEBIRD_RETURNFORMAT_OBJECT) {
      return (object) $rate;
    }
    return $rate;
  }