multiple-containers example does not work

[joverman-collective]

The multiple-containers example doesn't work after adding the additional_containers variable since it's used as such:

resource "aws_ecs_task_definition" "td" {
  container_definitions = jsonencode(concat(var.additional_containers, [module.container_definition.json_map_object]))
  ...

Only specifying additional_containers and not specifying the container directly makes us concat the additional_containers with essentially {}, which isn't a valid task definition. This gives the error:

Error: creating ECS Task Definition (my-td): operation error ECS: RegisterTaskDefinition, https response error StatusCode: 400, RequestID: 607d430b-b0ca-49c1-9ae3-c1f30ba8320d, ClientException: Container.name should not be null or empty.
│ 
│   with module.app.module.backend-service.module.ecs-fargate-task-definition["migration"].aws_ecs_task_definition.td,
│   on .terraform/modules/app.backend-service.ecs-fargate-task-definition/main.tf line 85, in resource "aws_ecs_task_definition" "td":
│   85: resource "aws_ecs_task_definition" "td" {

This should check to see if module.container_definition.json_map_object is "empty" before adding it to the container_definitions.