public function getMulti(array $keys, array &$tokens = null)
{
$keys = array_map(array($this, 'encodeKey'), $keys);
$return = $this->client->getMulti($keys, $tokens);
$keys = array_map(array($this, 'decodeKey'), array_keys($return));
$return = array_combine($keys, $return);
// HHVMs getMulti() returns null instead of empty array for no results,
// so normalize that
$tokens = $tokens ?: array();
$tokens = array_combine($keys, $tokens);
return $return ?: array();
}