diff --git a/main.tf b/main.tf
index 9252df4..bff1225 100644
--- a/main.tf
+++ b/main.tf
@@ -1,57 +1,70 @@
 variable "cmd" {
+  type        = string
   description = "The command used to create the resource."
 }
 
 variable "destroy_cmd" {
+  type        = string
   description = "The command used to destroy the resource."
+  default     = "true"
 }
 
 variable "account_id" {
+  type        = string
   description = "The account that holds the role to assume in. Will use providers account by default"
-  default     = "0"
+  default     = ""
 }
 
 variable "role" {
+  type        = string
   description = "The role to assume in order to run the cli command."
-  default     = "0"
+  default     = ""
 }
 
 variable "dependency_ids" {
   description = "IDs or ARNs of any resources that are a dependency of the resource created by this module."
-  type        = "list"
+  type        = list(string)
   default     = []
 }
 
 data "aws_caller_identity" "id" {}
 
 locals {
-  account_id      = "${var.account_id == 0 ? data.aws_caller_identity.id.account_id : var.account_id}"
+  account_id      = var.account_id == "" ? data.aws_caller_identity.id.account_id : var.account_id
   assume_role_cmd = "source ${path.module}/assume_role.sh ${local.account_id} ${var.role}"
 }
 
 resource "null_resource" "cli_resource" {
+  triggers = {
+    role            = var.role
+    cmd             = var.cmd
+    destroy_cmd     = var.destroy_cmd
+    assume_role_cmd = local.assume_role_cmd
+  }
   provisioner "local-exec" {
-    when    = "create"
-    command = "/bin/bash -c '${var.role == 0 ? "" : "${local.assume_role_cmd} && "}${var.cmd}'"
+    when    = create
+    command = "/bin/bash -c '${self.triggers.role == "" ? "" : "${self.triggers.assume_role_cmd} && "}${self.triggers.cmd == "" ? "true" : self.triggers.cmd}'"
   }
 
   provisioner "local-exec" {
-    when    = "destroy"
-    command = "/bin/bash -c '${var.role == 0 ? "" : "${local.assume_role_cmd} && "}${var.destroy_cmd}'"
+    when    = destroy
+    command = "/bin/bash -c '${self.triggers.role == "" ? "" : "${self.triggers.assume_role_cmd} && "}${self.triggers.destroy_cmd == "" ? "true" : self.triggers.destroy_cmd}'"
   }
 
   # By depending on the null_resource, the cli resource effectively depends on the existance
   # of the resources identified by the ids provided via the dependency_ids list variable.
-  depends_on = ["null_resource.dependencies"]
+  depends_on = [
+    null_resource.dependencies
+  ]
 }
 
 resource "null_resource" "dependencies" {
   triggers = {
-    dependencies = "${join(",", var.dependency_ids)}"
+    dependencies = join(",", var.dependency_ids)
   }
 }
 
 output "id" {
   description = "The ID of the null_resource used to provison the resource via cli. Useful for creating dependencies between cli resources"
-  value       = "${null_resource.cli_resource.id}"
+  value       = null_resource.cli_resource.id
 }
diff --git a/versions.tf b/versions.tf
new file mode 100644
index 0000000..bc7a146
--- /dev/null
+++ b/versions.tf
@@ -0,0 +1,8 @@
+terraform {
+  required_providers {
+    null = {
+      source  = "hashicorp/null"
+      version = "~> 3.1"
+    }
+  }
+}