private function processHistoricalResponse(Response $response)
{
if ($response->isOK()) {
$data = json_decode($response->getContent(true), true);
$values = array_map(array($this, 'float'), $data['val']);
array_pop($values);
// remove the last null value...
return new History(new DateTime($data['tm']), $values, $data['un'], (int) $data['dt']);
}
}