Panic when invoking function with --async option

[Takafumi Hirata]

Current Behavior

Invoking function with --async option causes panic.
Error logs are as follows:

log

❯ echo '{"Name":"lambroll"}' | lambroll invoke --region ap-northeast-1 --log-level trace --async
2020/01/13 21:51:30 [info] lambroll v0.3.2
2020/01/13 21:51:30 [debug] invoking function {
  FunctionName: "lambroll-sample",
  InvocationType: "Event",
  Payload: <binary> len 19
}

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x15f02a8]

goroutine 1 [running]:
github.com/fujiwara/lambroll.(*App).Invoke(0xc000081780, 0xc000089c90, 0xc0000a8e76, 0xc0000a8e77, 0x0, 0xc000089da0)
	/home/runner/work/lambroll/lambroll/invoke.go:69 +0x628
main._main(0xc000086058)
	/home/runner/work/lambroll/lambroll/cmd/lambroll/main.go:103 +0x26de
main.main()
	/home/runner/work/lambroll/lambroll/cmd/lambroll/main.go:17 +0x22

same function works as expected without --async option.

Cause

Panic is caused by dereferencing res.ExecutedVersion, which is not included in response when invocation type is Event.
It seems Lambda Invoke API returns only StatusCode when invocation type is Event.

cf.

• https://docs.aws.amazon.com/lambda/latest/dg/invocation-async.html
• https://docs.aws.amazon.com/cli/latest/reference/lambda/invoke.html

How to reproduce

1. init function
2. deploy function
3. invoke function with --async option

Environment

lambroll version: v0.3.2 ( and b9a4c02 built with go 1.13)
OS: macOS 10.14.6