public function get($primaryKey, $secondaryKey)
    {
        if (!isset($this->values[$primaryKey][$secondaryKey])) {
            throw new OutOfBoundsException(sprintf(
                'The key ("%s","%s") does not exist.',
                $primaryKey,
                $secondaryKey
            ));
        }

        return $this->values[$primaryKey][$secondaryKey];
    }