fix null variable

debian/main.tf

@@ -24,4 +24,5 @@ module "tf_debian_vm" {
   ca_host               = coalesce(var.ca_host, module.invariants.ca_host)
   memory                = var.memory
   data_disk             = var.data_disk
+  fixed_address         = var.fixed_address
 }

debian/variables.tf

@@ -56,3 +56,8 @@ variable "data_disk" {
   type    = string
   default = null
 }
+
+variable "fixed_address" {
+  type = string
+  default = ""
+}