Invalid index error when emrcontainers or step functions (sfn) are not enabled

[bdellegrazie]

Description

If, using the existing example, you disable the emrcontainers and/or step functions as follows:

# Controllers to enable
# ... other parts elided
enable_emrcontainers = false
enable_sfn = false

Then terraform responds with the following output:

│ Error: Invalid index
│ 
│   on .terraform/modules/eks_ack_addons/main.tf line 592, in module "emrcontainers":
│  592:     AmazonEmrContainers = aws_iam_policy.emrcontainers[0].arn
│     ├────────────────
│     │ aws_iam_policy.emrcontainers is empty tuple
│ 
│ The given key does not identify an element in this collection value: the collection has no elements.
╵
╷
│ Error: Invalid index
│ 
│   on .terraform/modules/eks_ack_addons/main.tf line 773, in module "sfn":
│  773:     AWSStepFunctionsIamPassRole = aws_iam_policy.sfnpasspolicy[0].arn
│     ├────────────────
│     │ aws_iam_policy.sfnpasspolicy is empty tuple
│ 
│ The given key does not identify an element in this collection value: the collection has no elements.

This is always reproducible with v2.0.0 of the provider (latest at time of writing)

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

Versions

• Module version: v2.0.0

• Terraform version: 1.5.2

• Provider version(s):

Terraform v1.5.2
on linux_amd64
+ provider registry.terraform.io/hashicorp/aws v5.6.2
+ provider registry.terraform.io/hashicorp/helm v2.10.1
+ provider registry.terraform.io/hashicorp/kubernetes v2.21.1

Reproduction Code

See example above in the description.
This is verifiable with the example code in this repository.

Expected behavior

Resources to be provisioned

Actual behavior

Error reported as above.

Terminal Output Screenshot(s)

Error reported as above.

Additional context

I believe this can easily be solved by either a conditional assignment:
(e.g.)

AmazonEmrContainers = var.enable_emrcontainers ? aws_iam_policy.emrcontainers[0].arn : null

or by the use of try:

AmazonEmrContainers = try(aws_iam_policy.emrcontainers[0].arn, null)