Bug: uncaught null message in version 1.3

[ZBeimford]

Expected Behavior

A message is sent via the 'begin' handler, my testing shows the message sent is 'null.'
Floop should probably catch this and send a meaningful error.

Current Behavior

Currently it fails with message
"2018/03/26 17:55:12 [INFO] Registered handler: phase=completed handler=gnatsd
2018/03/26 17:55:12 [INFO] Registered handler: phase=progress handler=gnatsd
2018/03/26 17:55:13 [INFO] Registered handler: phase=failed handler=gnatsd
2018/03/26 17:55:13 [INFO] Registered handler: phase=begin handler=gnatsd
panic: interface conversion: interface {} is nil, not *types.ChildResult

goroutine 1 [running]:
github.com/d3sw/floop.(*phaseHandler).Handle(0xc420114a00, 0xc4200f3560, 0x94f7c0, 0x5, 0xc420130390)
/Users/Todd/go/src/github.com/d3sw/floop/handler.go:58 +0x19e
github.com/d3sw/floop.(*Lifecycle).Begin(0xc4200dbb60, 0xc4200f3530, 0x0, 0x0)
/Users/Todd/go/src/github.com/d3sw/floop/lifecycle.go:110 +0x183
github.com/d3sw/floop.(*Floop).Start(0xc4200f3500, 0xc420017bf0, 0xc4200f3500, 0x0)
/Users/Todd/go/src/github.com/d3sw/floop/floop.go:81 +0xb7
main.(*CLI).run(0xc42004c820, 0xc420017b90, 0xc420017b30, 0xc420017ad0)
/Users/Todd/go/src/github.com/d3sw/floop/cmd/cli.go:138 +0x162
main.(*CLI).Run(0xc42004c820, 0x7, 0xc42000e0b0, 0x9)
/Users/Todd/go/src/github.com/d3sw/floop/cmd/cli.go:111 +0x4b
main.main()
/Users/Todd/go/src/github.com/d3sw/floop/cmd/main.go:20 +0xfc"

Steps to Reproduce (for bugs)

1. Send a null through a handler using version 1.3

Context

Your Environment

Alpine docker container

• Product Version: openjdk:8u121-jdk-alpine