yum/dnf aborts with Error: GetValue(): Value not set

Issue

Using yum or dnf with the sub-commands list or update gives the error below:

# yum list
Updating Subscription Management repositories.
Error: GetValue(): Value not set

dnf.log shows a python traceback:

2020-10-14T11:02:55Z DEBUG User-Agent: constructed: 'libdnf (Red Hat Enterprise Linux 8.2; generic; Linux.x86_64)'
2020-10-14T11:02:55Z DEBUG repo: downloading from remote: rhel-8-for-x86_64-appstream-rpms
2020-10-14T11:02:55Z DDEBUG Cleaning up.
2020-10-14T11:02:55Z SUBDEBUG 
Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/dnf/repo.py", line 573, in load
    ret = self._repo.load()
  File "/usr/lib64/python3.6/site-packages/libdnf/repo.py", line 394, in load
    return _repo.Repo_load(self)
RuntimeError: GetValue(): Value not set

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 65, in main
    return _main(base, args, cli_class, option_parser_class)
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 98, in _main
    return cli_run(cli, base)
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 114, in cli_run
    cli.run()
  File "/usr/lib/python3.6/site-packages/dnf/cli/cli.py", line 1143, in run
    self._process_demands()
  File "/usr/lib/python3.6/site-packages/dnf/cli/cli.py", line 833, in _process_demands
    load_available_repos=self.demands.available_repos)
  File "/usr/lib/python3.6/site-packages/dnf/base.py", line 392, in fill_sack
    self._add_repo_to_sack(r)
  File "/usr/lib/python3.6/site-packages/dnf/base.py", line 137, in _add_repo_to_sack
    repo.load()
  File "/usr/lib/python3.6/site-packages/dnf/repo.py", line 580, in load
    raise dnf.exceptions.RepoError(str(e))
dnf.exceptions.RepoError: GetValue(): Value not set
2020-10-14T11:02:55Z CRITICAL Error: GetValue(): Value not set