break-apart logic for readability

Author: abeluck

deprecated.tf

@@ -7,7 +7,14 @@ locals {
   cloudfront_access_log_include_cookies = var.log_include_cookies == null ? var.cloudfront_access_log_include_cookies : var.log_include_cookies
   cloudfront_access_log_prefix          = var.log_prefix == null ? var.cloudfront_access_log_prefix : var.log_prefix
 
-  deployment_principals = var.deployment_principal_arns == null ? var.deployment_principals : { for arn, path_prefix in var.deployment_principal_arns : arn => { "arn" : arn, "path_prefix" : path_prefix } }
+  deployment_principals_from_deprecated_deployment_principal_arns = {
+    for arn, path_prefix in coalesce(var.deployment_principal_arns, {}) :
+    arn => {
+      "arn" : arn,
+      "path_prefix" : path_prefix
+    }
+  }
+  deployment_principals = var.deployment_principal_arns == null ? var.deployment_principals : local.deployment_principals_from_deprecated_deployment_principal_arns
 
   # New variables, but declare them here for consistency
   cloudfront_access_log_create_bucket = var.cloudfront_access_log_create_bucket