add test for nil case
add test for nil case

ricardclau/packer,rnaveiras/packer,grubernaut/packer,mitchellh/packer,paulmey/packer,dave2/packer,bryson/packer,pecigonzalo/packer,timsutton/packer,bryson/packer,ricardclau/packer,dave2/packer,hashicorp/packer,bryson/packer,mitchellh/packer,rnaveiras/packer,paulmey/packer,hashicorp/packer,dave2/packer,timsutton/packer,timsutton/packer,grubernaut/packer,grubernaut/packer,dave2/packer,bryson/packer,rnaveiras/packer,ricardclau/packer,grubernaut/packer,hashicorp/packer,mitchellh/packer,hashicorp/packer,bryson/packer,rnaveiras/packer,paulmey/packer,mitchellh/packer,bryson/packer,ricardclau/packer,pecigonzalo/packer,mitchellh/packer,pecigonzalo/packer,timsutton/packer,dave2/packer,timsutton/packer,grubernaut/packer,paulmey/packer,dave2/packer,pecigonzalo/packer,grubernaut/packer,ricardclau/packer,rnaveiras/packer,paulmey/packer,ricardclau/packer,paulmey/packer,timsutton/packer,rnaveiras/packer