Can't associate the range as a secondary range to VPC with terraform

resource "aws_vpc_ipv4_cidr_block_association" "eks_vpc_secondary_cidr" {
  vpc_id = module.eks-vpc.vpc_id
  cidr_block = ""

Error: expected "cidr_block" to contain a network Value with between 16 and 28 significant bits, got: 10

I’m using terraform “0.13.5” and aws provider “3.16.0”,

As far as I know “” is a perfectly valid secondary CIDR for VPC and I have it configured it in the past (via the AWS console). It’s is used frequently when setting up EKS with CNI custom networking (where the pods are given IPs in the range).

See Amazon EKS now supports additional VPC CIDR blocks

It’s the same with terraform 0.15.4 and aws provider 3.42.0 which are the lastest versions now (2021-05-31)

I filled a GitHub issue 19595.