Define local.validation_domains properly.

[plutino]

Description

We came across this bug when upgrading to Terraform 0.12.

We use a pre-created ACM cert when using the terraform-aws-modules/atlantis/aws module. During terraform plan, we got this error:

Error: Invalid index

  on .terraform/modules/atlantis.acm/terraform-aws-modules-terraform-aws-acm-566067c/main.tf line 6, in locals:
   6:   validation_domains = [for k, v in aws_acm_certificate.this[0].domain_validation_options : tomap(v) if contains(local.distinct_domain_names, v.domain_name)]
    |----------------
    | aws_acm_certificate.this is empty tuple

The given key does not identify an element in this collection value.

This appears to be caused by resource count being zero for aws_acm_certificate.this, and thus aws_acm_certificate.this[0] is an invalid reference.

This PR fix this by setting local.validation_domains to an empty list when var.create_certificate is false.

[richardcase]

Would be great to get this merged

[antonbabenko]

Thanks a lot, @plutino !

This works as expected, I have just released v2.4.0 of this module.

[plutino]

Thank for the quick action @antonbabenko. Now we can do another PR for the aws-atlantis module to use this latest version so that we can continue our terraform 0.12 upgrade.

[antonbabenko]

I've just done it. Please, use v2.3.0 of terraform-aws-atlantis module.

[plutino]

wow, thank you!

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