Repository: kubernetes-client/python
Issue: listing all pods leads to "sources must not be None" error in v1_projected_volume_source.py

**What happened (please include outputs or screenshots)**:
```
Traceback (most recent call last):
  File "/opt/autoscaler/ski_autoscaler/lifecycle_manager.py", line 566, in lifecycle_manager
    main(
  File "/opt/autoscaler/ski_autoscaler/lifecycle_manager.py", line 478, in main
    asg_pods = kube_filter.pods_in_asg_filter(kube_filter.get_all_pods(), asg_nodes)
  File "/opt/autoscaler/ski_utils/kube_filter.py", line 86, in get_all_pods
    result = v1.list_pod_for_all_namespaces(watch=False)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api/core_v1_api.py", line 14098, in list_pod_for_all_namespaces
    (data) = self.list_pod_for_all_namespaces_with_http_info(**kwargs)  # noqa: E501
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api/core_v1_api.py", line 14179, in list_pod_for_all_namespaces_with_http_info
    return self.api_client.call_api(
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 340, in call_api
    return self.__call_api(resource_path, method,
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 184, in __call_api
    return_data = self.deserialize(response_data, response_type)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 256, in deserialize
    return self.__deserialize(data, response_type)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 295, in __deserialize
    return self.__deserialize_model(data, klass)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 636, in __deserialize_model
    kwargs[attr] = self.__deserialize(value, attr_type)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 272, in __deserialize
    return [self.__deserialize(sub_data, sub_kls)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 272, in <listcomp>
    return [self.__deserialize(sub_data, sub_kls)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 295, in __deserialize
    return self.__deserialize_model(data, klass)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 636, in __deserialize_model
    kwargs[attr] = self.__deserialize(value, attr_type)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 295, in __deserialize
    return self.__deserialize_model(data, klass)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 636, in __deserialize_model
    kwargs[attr] = self.__deserialize(value, attr_type)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 272, in __deserialize
    return [self.__deserialize(sub_data, sub_kls)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 272, in <listcomp>
    return [self.__deserialize(sub_data, sub_kls)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 295, in __deserialize
    return self.__deserialize_model(data, klass)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 636, in __deserialize_model
    kwargs[attr] = self.__deserialize(value, attr_type)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 295, in __deserialize
    return self.__deserialize_model(data, klass)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/api_client.py", line 638, in __deserialize_model
    instance = klass(**kwargs)
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/models/v1_projected_volume_source.py", line 52, in __init__
    self.sources = sources
  File "/usr/local/lib/python3.8/site-packages/kubernetes/client/models/v1_projected_volume_source.py", line 98, in sources
    raise ValueError("Invalid value for `sources`, must not be `None`")  # noqa: E501
ValueError: Invalid value for `sources`, must not be `None`
```

**What you expected to happen**:
return a list of all pods

**How to reproduce it (as minimally and precisely as possible)**:
One of my clusters does it every time, all the time, starting today. My other clusters do NOT exhibit the same behavior

**Anything else we need to know?**:

**Environment**:
- Kubernetes version (`kubectl version`): v1.17.12-eks-7684af
- OS (e.g., MacOS 10.13.6): ubuntu 20.04
- Python version (`python --version`) 3.8 and 3.9
- Python client version (`pip list | grep kubernetes`) 11.0.0 and 17.17.0


Changed files:
kubernetes/client/models/v1_projected_volume_source.py

diff --git a/kubernetes/client/models/v1_projected_volume_source.py b/kubernetes/client/models/v1_projected_volume_source.py
index a2f41d730..ab8c66a26 100644
--- a/kubernetes/client/models/v1_projected_volume_source.py
+++ b/kubernetes/client/models/v1_projected_volume_source.py
@@ -99,9 +99,6 @@ class V1ProjectedVolumeSource(object):
         :param sources: The sources of this V1ProjectedVolumeSource.  # noqa: E501
         :type: list[V1VolumeProjection]
         """
-        if self.local_vars_configuration.client_side_validation and sources is None:  # noqa: E501
-            raise ValueError("Invalid value for `sources`, must not be `None`")  # noqa: E501
-
         self._sources = sources
 
     def to_dict(self):