function getSetValues($key)
    {
        if (isset($this->configuration_info[$key]) &&
            isset($this->configuration_info[$key]['type']) &&
            $this->configuration_info[$key]['type'] == 'set')
        {
            $valid_set = $this->configuration_info[$key]['valid_set'];
            reset($valid_set);
            if (key($valid_set) === 0) {
                return $valid_set;
            }

            return array_keys($valid_set);
        }

        return null;
    }