kubernetes: kubectl 1.8 cannot validate simple namespace yml

Is this a BUG REPORT or FEATURE REQUEST?:

/kind bug

What happened: kubectl 1.8.0 fails to validate a simple namespace yml:

apiVersion: v1
kind: Namespace
metadata:
  name: foo

Same problem if I use json (which is how I first noticed, it trying to restore from a get ns -ojson --export )

What you expected to happen: kubectl to validate and pass it on to the cluster

How to reproduce it (as minimally and precisely as possible):

1. Create foo.yml with the content above
2. kubectl apply -f foo.yml (or create if you prefer) with kubectl 1.8.0 - it fails validation
3. kubectl apply -f foo.yml with kubectl 1.7.5 - it works

Anything else we need to know?:

Environment:

• Kubernetes version (use kubectl version):

Client Version: version.Info{Major:"1", Minor:"8", GitVersion:"v1.8.0", GitCommit:"6e937839ac04a38cac63e6a7a306c5d035fe7b0a", GitTreeState:"clean", BuildDate:"2017-09-28T22:57:57Z", GoVersion:"go1.8.3", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"7", GitVersion:"v1.7.0", GitCommit:"d3ada0119e776222f11ec7945e6d860061339aad", GitTreeState:"clean", BuildDate:"2017-07-26T00:12:31Z", GoVersion:"go1.8.3", Compiler:"gc", Platform:"linux/amd64"}

For the working 1.7.5:

Client Version: version.Info{Major:"1", Minor:"7", GitVersion:"v1.7.5", GitCommit:"17d7182a7ccbb167074be7a87f0a68bd00d58d97", GitTreeState:"clean", BuildDate:"2017-08-31T09:14:02Z", GoVersion:"go1.8.3", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"7", GitVersion:"v1.7.0", GitCommit:"d3ada0119e776222f11ec7945e6d860061339aad", GitTreeState:"clean", BuildDate:"2017-07-26T00:12:31Z", GoVersion:"go1.8.3", Compiler:"gc", Platform:"linux/amd64"}

• Cloud provider or hardware configuration**:

Running on minikube to replicate

• OS (e.g. from /etc/os-release):

From minikube:

$ cat /etc/os-release
NAME=Buildroot
VERSION=2017.02
ID=buildroot
VERSION_ID=2017.02
PRETTY_NAME="Buildroot 2017.02"

• Kernel (e.g. uname -a):

$ uname -a
Linux minikube 4.9.13 #1 SMP Tue Jul 18 22:17:02 UTC 2017 x86_64 GNU/Linux

• Install tools:

minikube

• Others:

Summary:

/tmp # cat foo.yml
apiVersion: v1
kind: Namespace
metadata:
  name: foo
/tmp # kubectl175 apply -f foo.yml
namespace "foo" configured
/tmp # kubectl180 apply -f foo.yml
error: error validating "foo.yml": error validating data: unknown object type schema.GroupVersionKind{Group:"", Version:"v1", Kind:"Namespace"}; if you choose to ignore these errors, turn validation off with --validate=false