Fix EKS release version handle null default correctly

Author: pst

aws/_modules/eks/node_pool/launch_template.tf

@@ -9,7 +9,7 @@ locals {
   is_gpu             = length(data.aws_ec2_instance_type.current.gpus) > 0
   ami_name           = local.is_gpu ? "amazon-linux-2-gpu" : local.cpu_ami_name
   ami_release_prefix = local.is_gpu ? "amazon-eks-gpu-node" : "amazon-eks-node"
-  ami_release_date   = split("-", var.ami_release_version)[1]
+  ami_release_date   = var.ami_release_version == null ? "" : split("-", var.ami_release_version)[1]
   ami_release_name   = var.ami_release_version == null ? "recommended" : "${local.ami_release_prefix}-${var.kubernetes_version}-v${local.ami_release_date}"
 }