panic/nil for empty command in included taskfile

[philpennock]

This issue is a mix of #338 and #612 -- an empty task causes a crash, but only if the empty task is in an included taskfile.

• Task version: 3.11.0
  • Task version: v3.11.0 (h1:eCcCe1cKyta4YnGQYLo2FriPS9h7fFS8XBVW6QvWEV4=)
• Operating System:
  • Ubuntu 20.04 LTS
  • task installed with go install github.com/go-task/task/v3/cmd/task@latest, Go 1.17.7

Example Taskfile showing the issue

1. Taskfile.yaml:

   version: '3'
   includes:
     a: taskfile-inc.yaml
   

2. taskfile-inc.yaml

   version: '3'
   tasks:
     bar:
   

$ task -l
panic: runtime error: invalid memory address or nil pointer dereference
[...]

[tylermmorton]

Thank you for reporting this. I will see if I can add a fix and test coverage in my PR at #656.