Terraform中如何将sensitive_labels设为可选dynamic block？

我尝试将sensitive_labels动态块设置为可选属性但未成功，现有代码如下：

现有代码 #

variables.tf #

variable "notification_channels" {
  type = any
}

variable "project_id" {
  type = string
}

main.tf（初始报错版本） #

resource "google_monitoring_notification_channel" "channels" {
  project      = var.project_id
  for_each     = { for k, v in var.notification_channels : k => v }
  type         = each.value.type
  display_name = each.value.display_name
  description  = each.value.description
  labels       = each.value.labels
  enabled      = each.value.enabled

  dynamic "sensitive_labels" {
    for_each = each.value.sensitive_labels != {} ? [each.value.sensitive_labels] : []
    content {
      auth_token = lookup(sensitive_labels.value, "auth_token", null)
    }
  }
}

dev.tfvars #

notification_channels = [
  {
    type         = "email"
    display_name = "a channel to send emails"
    description  = "a nice channel"
    labels = {
      email_address = "HeyThere@something.com"
    }
    enabled          = true
    sensitive_labels = {} // 此条目无报错
  },
  {
    type         = "email"
    display_name = "HeyThere Email"
    description  = "a channel to send emails"
    labels = {
      email_address = "HeyThere2@something.com"
    }
    enabled          = true
  }
]

报错信息 #

Error: Unsupported attribute

on notification_channels.tf line 11, in resource "google_monitoring_notification_channel" "channels":
11: for_each = each.value.sensitive_labels != {} ? [each.value.sensitive_labels] : []
│ ├────────────────
each.value is object with 5 attributes

This object does not have an attribute named "sensitive_labels".

临时解决方案（lookup实现） #

我用lookup方法实现了功能，但感觉不够优雅：

resource "google_monitoring_notification_channel" "channels" {
  project      = var.project_id
  for_each     = { for k, v in var.notification_channels : k => v }
  type         = each.value.type
  display_name = each.value.display_name
  description  = each.value.description
  labels       = each.value.labels
  enabled      = each.value.enabled

  dynamic "sensitive_labels" {
    for_each = lookup(each.value, "sensitive_labels", {})
    content {
      auth_token = lookup(sensitive_labels.value, "auth_token", null)
    }
  }
}

请问有没有更优的实现方式？

内容的提问来源于stack exchange，提问作者MassHysteria