Difference between null and empty value

Terraform
1

I am getting error if I am using null default value

variable "data" {
   type = object({
     foo = string
   })
}

variable "optional_data" {
  type = object({
    custom_image_name = string
    custom_image_resource_group_name = string
  })

  default = {
    custom_image_name = null
    custom_image_resource_group_name = null
  }
}

locals {
   merged_data = "${merge(var.data, var.optional_data)}"
}


data "azurerm_image" "image" {
  name                = "${local.merged_data.custom_image_name}"
  resource_group_name = "${local.merged_data.custom_image_resource_group_name}"

  count = "${local.merged_data.custom_image_name != "" && local.merged_data.custom_image_resource_group_name != "" ? 1 : 0 }"

}

will result in

Error: "resource_group_name": required field is not set

If I change default value of custom_image_resource_group_name

variable "optional_data" {
  type = object({
    custom_image_name = string
    custom_image_resource_group_name = string
  })

  default = {
    custom_image_name = null
    custom_image_resource_group_name = ""
  }
}

it will work…

Is it intended ?
How can I use null in this use case? Is it even possible?
Thanks

2

Hello @lukasmrtvy,

null is equivalent to “unset”. In the Azure provider, the azurerm_image data source requires resource_group_name to be set. This is why an empty string will work but not null (which means the parameter is unset).

I’ve found this reference to be useful for helping me understand the null value!