Client does not accept null subsets in endpoint objects

[hanikesn]

Neither version 4.0.0 nor 5.0.0 accept Endpoint objects from kubernetes 1.8, which don't have any endpoints defined. According to the official documentation json clients should accept both empty arrays as well as null values.

See:

Protobuf serialization does not distinguish between [] and null.
https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG-1.8.md#action-required-2

apiVersion: v1
kind: Endpoints
metadata:
  creationTimestamp: 2017-12-08T13:33:24Z
  labels:
    app: zero-test
    expose: http
  name: zero-test
  namespace: default
  resourceVersion: "40308257"
  selfLink: /api/v1/namespaces/default/endpoints/zero-test
  uid: 5d47e6c7-dc1c-11e7-85ba-0244ea825020
subsets: null

  File "/home/steffen/dev/ingress-nginx-plus/env/lib/python3.6/site-packages/kubernetes/client/models/v1_endpoints.py", line 64, in __init__
    self.subsets = subsets
  File "/home/steffen/dev/ingress-nginx-plus/env/lib/python3.6/site-packages/kubernetes/client/models/v1_endpoints.py", line 156, in subsets
    raise ValueError("Invalid value for `subsets`, must not be `None`")
ValueError: Invalid value for `subsets`, must not be `None`

[mbohlool]

dup of #376