panic in function implementation: must not call MapVal with empty map

[ipmb]

Terraform Version

Terraform v0.13.0-beta2

Terraform Configuration Files

module "client_vpc" {
  source          = "terraform-aws-modules/vpc/aws"
  name            = "clients"
  azs             = ["us-east-1a", "us-east-1b", "us-east-1c"]
  cidr            = "10.3.0.0/16"
  public_subnets  = ["10.3.0.0/24", "10.3.1.0/24", "10.3.2.0/24"]
  private_subnets = ["10.3.100.0/22", "10.3.104.0/22", "10.3.108.0/22"]

  enable_dns_hostnames                            = true
  enable_flow_log                                 = true
  flow_log_traffic_type                           = "REJECT"
  create_flow_log_cloudwatch_iam_role             = true
  create_flow_log_cloudwatch_log_group            = true
  flow_log_cloudwatch_log_group_retention_in_days = 14
  flow_log_cloudwatch_log_group_name_prefix       = "/aws/vpc-flow-logs/"
}

Debug Output

Crash Output

https://gist.github.com/ipmb/fcac64a32f0cac1d50d59062dbaca21e

Expected Behavior

Not crash :)

Actual Behavior

Panic

Steps to Reproduce

terraform plan

Additional Context

References

[jurgenweber]

I am using the same module, I do not get this error on plan but when I am import a completely unrelated resource. Seems a bit weird to me.

$ tf import module.secrets.aws_kms_key.tf_enc_key bc901111ade7-7e41-42111111a-86cf-1234
module.secrets.aws_kms_key.tf_enc_key: Importing from ID "bc901111ade7-7e41-42111111a-86cf-1234"...
module.secrets.aws_kms_key.tf_enc_key: Import prepared!
  Prepared aws_kms_key for import
module.secrets.aws_kms_key.tf_enc_key: Refreshing state... [id=bc901111ade7-7e41-42111111a-86cf-1234]

Error: Error in function call

  on .terraform/modules/cluster.vpc/terraform-aws-vpc-2.44.0/main.tf line 20, in locals:
  20:   vpce_tags = merge(
  21:     var.tags,
  22:     var.vpc_endpoint_tags,
  23:   )
    |----------------
    | var.tags is empty map of string
    | var.vpc_endpoint_tags is empty map of string

I also have set for the module inputs, tags and vpc_endpoint_tags so their should be maps/content.

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