Error 'NoneType' object is not iterable with Kubernetes Version 1.19

[shreyaskarnik]

First of all, this project has helped me a lot in performing rolling upgrades of nodes on our Kubernetes cluster.
I have noticed that on Kubernetes Version 1.19 and above I get the following error message and the rolling upgrade process ends.

2021-04-22 15:35:16,761 INFO     Checking k8s expected nodes are online after asg scaled up... 
2021-04-22 15:35:16,787 ERROR    'NoneType' object is not iterable

I was able to fix this by upgrading the version of Kubernetes client to the latest version on pypi and get around this issue.
I am opening this issue to help others who might have been in a similar situation.