driver.go
func (c HubConfig) GetString(key string, defval string) string {
	val, ok := c[key]
	if ok {
		s, ok := val.(string)
		if ok && len(s) > 0 {
			return s
		}
		// TODO only primitive types
		return fmt.Sprintf("%s", val)
	}
	return defval
}
func (c HubConfig) GetString(key string, defval string) string {
	val, ok := c[key]
	if ok {
		s, ok := val.(string)
		if ok && len(s) > 0 {
			return s
		}
		// TODO only primitive types
		return fmt.Sprintf("%s", val)
	}
	return defval
}
// GetString property.