Invalid function argument error when using merge method

[yuekui]

Description

To conditionally create an endpoint, we plan to use a merge method combined with a ternary expression. However, this approach may lead to an 'Invalid function argument' error because the lookup function might return a null value, which differs from the expected default type [].

• [x] ✋ I have searched the open/closed issues and my issue is not listed.

Versions

• Terraform version: 1.5.7
• Provider version(s): hashicorp/aws v5.48.0

Reproduction Code [Required]

locals {
  is_additional_task_needed = true
}

module "dms_aurora_postgresql_aurora_mysql" {
  # Endpoints
  endpoints = merge({
    postgresql-destination = {
      ...
    },local.is_additional_task_needed ? {
    mysql-source = {
      database_name = "foo"
      ...
    } } : {}
  )

Expected behavior

Endpoints should be created successfully

Actual behavior

Invalid function argument errors were raised when trying to lookup settings of each value

Terminal Output Screenshot(s)

Additional context

I've created a PR and added the conditional endpoints in example

[github-actions[bot]]

This issue has been automatically marked as stale because it has been open 30 days with no activity. Remove stale label or comment or this issue will be closed in 10 days

[yuekui]

Hi @bryantbiggs , it would be great if you could review this when you have a chance. Thanks!

[github-actions[bot]]

This issue has been automatically marked as stale because it has been open 30 days with no activity. Remove stale label or comment or this issue will be closed in 10 days

[yuekui]

Just re-opened the PR, waiting for review

[bryantbiggs]

this looks like a dynamic workspace use issue, not a module issue. if you want to do this sort of dynamic "if this, then that", then you should use map comprehension instead of a conditional on the map object