code: func (cfg *Config) CheckAndSetDefaults() error {
  	// table is not configured?
  	if cfg.Tablename == "" {
  		return trace.BadParameter("DynamoDB: table_name is not specified")
  	}
  	if cfg.ReadCapacityUnits == 0 {
  		cfg.ReadCapacityUnits = DefaultReadCapacityUnits
  	}
  	if cfg.WriteCapacityUnits == 0 {
  		cfg.WriteCapacityUnits = DefaultWriteCapacityUnits
  	}
  	if cfg.RetentionPeriod == 0 {
  		cfg.RetentionPeriod = DefaultRetentionPeriod
  	}
  	if cfg.Clock == nil {
  		cfg.Clock = clockwork.NewRealClock()
  	}
  	if cfg.UIDGenerator == nil {
  		cfg.UIDGenerator = utils.NewRealUID()
  	}
  	return nil
  }
docs: // CheckAndSetDefaults is a helper returns an error if the supplied configuration
  // is not enough to connect to DynamoDB