如何测试从AWS开发工具包找不到的结果？

I am a beginner in Go and am starting to use the AWS SDK.

I want to fetch some EC2 fields by looking for a tag using DescribeInstances. That works well. But if I use a tag that does not exist as parameter I get an empty struct as response:

{

}

I tried to test the result with nil and using unsafe.Sizeof(), but I don't get nil value or 0 value. What would be the correct way to do it? Thanks!

edit: I found a way to check. Because the aws api is inconsistent, sometimes it returns errors sometimes it does not. So for this sparticular call I test the size of the []*ec2.Reservation that is returned:

result, err := ec2Svc.DescribeInstances(input)
if len(result.Reservations) == 0 {
  fmt.Println("Nothing found for this tag")
  fmt.Println(err)
} else {
  for _, instance := range result.Reservations[0].Instances {
    return *instance.VpcId
  }
}