Error: Missing resource instance key

[apxela]

Hello,

I want to do some tests with terraform-aws-efs-backup module in version 0.9.0. I have this code:
`module "efs_backup" {
source = "git::https://github.com/cloudposse/terraform-aws-efs-backup.git?ref=master"

name = "${var.name}"
stage = "${var.stage}"
namespace = "${var.namespace}"
vpc_id = "${var.vpc_id}"
efs_mount_target_id = "${var.efs_mount_target_id}"
use_ip_address = "false"
noncurrent_version_expiration_days = "${var.noncurrent_version_expiration_days}"
ssh_key_pair = "${var.ssh_key_pair}"
datapipeline_config = "${var.datapipeline_config}"
modify_security_group = "true"
}

output "efs_backup_security_group" {
value = "${module.efs_backup.security_group_id}"
}with these variables:variable "name" {
default = "jira-efs"
}

variable "stage" {
default = "stage"
}

variable "namespace" {
default = "namespace"
}

variable "vpc_id" {
default = "vpc-02c0d010183c3c1ce"
}

variable "efs_mount_target_id" {
default = "fs-2c057de4"
}

variable "noncurrent_version_expiration_days" {
default = "30"
}

variable "ssh_key_pair" {}

variable "datapipeline_config" {
type = "map"
default = {
instance_type = "t2.micro"
email = ""
period = "24 hours"
timeout = "60 Minutes"
}
}`

when I launched terraform plan I got this error multiple times with all the attributes:

`Error: Missing resource instance key

on .terraform/modules/efs_backup.backups_label/outputs.tf line 2, in output "id":
2: value = "${null_resource.default.triggers.id}"

Because null_resource.default has "count" set, its attributes must be accessed
on specific instances.

For example, to correlate with indices of a referring resource, use:
null_resource.default[count.index]`

I am pretty new with terraform, so probably I am missing something, but after readinng some posts I think it could be related with the new version of terrform (I am using version 0.12).

Thank you very much for your work!

Regards