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