fix: Prevent an error when VPC Flow log log_group and role is not created (#844)

Author: air3ijai

vpc-flow-logs.tf

@@ -5,8 +5,8 @@ locals {
   create_flow_log_cloudwatch_iam_role  = local.enable_flow_log && var.flow_log_destination_type != "s3" && var.create_flow_log_cloudwatch_iam_role
   create_flow_log_cloudwatch_log_group = local.enable_flow_log && var.flow_log_destination_type != "s3" && var.create_flow_log_cloudwatch_log_group
 
-  flow_log_destination_arn = local.create_flow_log_cloudwatch_log_group ? aws_cloudwatch_log_group.flow_log[0].arn : var.flow_log_destination_arn
-  flow_log_iam_role_arn    = var.flow_log_destination_type != "s3" && local.create_flow_log_cloudwatch_iam_role ? aws_iam_role.vpc_flow_log_cloudwatch[0].arn : var.flow_log_cloudwatch_iam_role_arn
+  flow_log_destination_arn = local.create_flow_log_cloudwatch_log_group ? try(aws_cloudwatch_log_group.flow_log[0].arn, null) : var.flow_log_destination_arn
+  flow_log_iam_role_arn    = var.flow_log_destination_type != "s3" && local.create_flow_log_cloudwatch_iam_role ? try(aws_iam_role.vpc_flow_log_cloudwatch[0].arn, null) : var.flow_log_cloudwatch_iam_role_arn
 }
 
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