fix: create_rules = false causes error (terraform-aws-modules#19)

Author: sigmasternchen

outputs.tf

@@ -24,16 +24,12 @@ output "eventbridge_permission_ids" {
 # EventBridge Rule
 output "eventbridge_rule_ids" {
   description = "The EventBridge Rule IDs created"
-  value = {
-    for p in sort(keys(var.rules)) : p => aws_cloudwatch_event_rule.this[p].id
-  }
+  value       = var.create_rules ? { for p in sort(keys(var.rules)) : p => aws_cloudwatch_event_rule.this[p].id } : {}
 }
 
 output "eventbridge_rule_arns" {
   description = "The EventBridge Rule ARNs created"
-  value = {
-    for p in sort(keys(var.rules)) : p => aws_cloudwatch_event_rule.this[p].arn
-  }
+  value       = var.create_rules ? { for p in sort(keys(var.rules)) : p => aws_cloudwatch_event_rule.this[p].arn } : {}
 }
 
 # IAM Role