Why does subscription-manager fails with "TypeError: 'NoneType' object has no attribute '__getitem__'"?

Issue

On attempting to list all of the subscriptions that are compatible with a system, using subscription manager, below errors are seen:

# subscription-manager list
Traceback (most recent call last):
  File "/sbin/subscription-manager", line 9, in <module>
    load_entry_point('subscription-manager==1.21.10', 'console_scripts', 'subscription-manager')()
  File "/usr/lib64/python2.7/site-packages/subscription_manager/scripts/subscription_manager.py", line 85, in main
    return managercli.ManagerCLI().main()
  File "/usr/lib64/python2.7/site-packages/subscription_manager/managercli.py", line 2667, in main
    ret = CLI.main(self)
  File "/usr/lib64/python2.7/site-packages/subscription_manager/cli.py", line 183, in main
    return cmd.main()
  File "/usr/lib64/python2.7/site-packages/subscription_manager/managercli.py", line 501, in main
    return_code = self._do_command()
  File "/usr/lib64/python2.7/site-packages/subscription_manager/managercli.py", line 2311, in _do_command
    installed_products = products.InstalledProducts(self.cp).list(self.options.filter_string)
  File "/usr/lib64/python2.7/site-packages/rhsmlib/services/products.py", line 50, in list
    sorter = inj.require(inj.CERT_SORTER)
  File "/usr/lib64/python2.7/site-packages/subscription_manager/injection.py", line 106, in require
    return FEATURES.require(feature, *args, **kwargs)
  File "/usr/lib64/python2.7/site-packages/subscription_manager/injection.py", line 80, in require
    self.providers[feature] = provider(*args, **kwargs)
  File "/usr/lib64/python2.7/site-packages/subscription_manager/cert_sorter.py", line 323, in __init__
    self.update_product_manager()
  File "/usr/lib64/python2.7/site-packages/subscription_manager/cert_sorter.py", line 355, in update_product_manager
    consumer_identity.uuid)
  File "/usr/lib64/python2.7/site-packages/subscription_manager/cache.py", line 170, in update_check
    if self.has_changed() or force:
  File "/usr/lib64/python2.7/site-packages/subscription_manager/cache.py", line 475, in has_changed
    products = cached['products']
TypeError: 'NoneType' object has no attribute '__getitem__'