How do I make a block optional in a module?

I have this resource in my module: https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/compute_router

I merely want to make advertised_ip_ranges optional via a variable.

I my module I do this:

resource "google_compute_router" "my-router" {
  .....
  bgp {
    .....
    advertised_ip_ranges = var.advertised_ip_ranges

I tried the following, but nothing is working

• setting var.advertised_ip_ranges = {} throws this error:

  An argument named "advertised_ip_ranges" is not expected here. Did you mean to define a block of type "advertised_ip_ranges"?

• setting var.advertised_ip_ranges = null throws the same error.

I just want to be able to ignore and not set advertised_ip_ranges via the variable.

You can set it based on a variable, but you'll need to use dynamic.

For example:

variable "advertised_ip_ranges" {
  type    = set(map(string))
  default = []

  # Requires Terraform 1.1+
  # Other option is to default to `null`, and add check in `dynamic`.
  nullable = false
}

resource "google_compute_router" "my_router" {
  bgp {
    dynamic "advertised_ip_ranges" {
      for_each = var.advertised_ip_ranges
      # Without `nullable`:
      # for_each = coalesce(var.advertised_ip_ranges, [])

      content {
        # Mandatory
        range = advertised_ip_ranges.value.range
        # Optional
        description = lookup(advertised_ip_ranges.value, "description", null)
      }
    # ...
  }
  # ...
}